Micro System FAQ:

This FAQ will answer the questions you have when you’re thinking about purchasing a do-it-myself plans package (from us) or kit aquaponics system (from someone else; we don’t sell kits). This is not intended to address questions about construction, startup, and operation that you will have when you’re actually building and operating your system. The Micro System FREE FORUM addresses those questions, in detail and in depth. Please email us pictures of YOUR Micro System, both under construction and with vegetables growing in it; we will put a page on this site with a gallery of users’ Micro System photos when we have collected enough.

  1. What are the Micro System's best applications?

    It's ideal for those concerned about electrical consumption and energy efficiency who are on alternate power. It's ideal for classroom learning situations and small schools with limited funding who want to investigate aquaponics with a productive and stable small system. It's perfect for those with a small family (2-4 persons) who wish to grow a large part of their own produce each month.

  2. What does the Micro System cost to run?

    It operates on 15 Kw/hours of electricity (about $1.80) per month; it uses 5 pounds of fish food (about $2.25), and another $5-6 worth of seeds and planting media per month, for a $10 per month total. Your return is from 40-60 pounds of organic produce and 2-3 pounds of fish per month. At average prices for the produce it pays for its cost of plans and construction in three to four months.

  3. Do you have to be technically-minded to run a Micro System?

    Not at all. The operations manual provided with the package walks you through operating a Micro System with a checklist. If you simply follow the checklist, it's easy. There are also answers to common Micro System problems that users often have (most often when they didn't entirely read the manual). Working with aquaponics is kind of like math; when you first started working with those numbers (remember, you were only three feet tall?), it was hard adding 3 and 6. Now you do it without thinking about it.

    In practice, it's just feeding the fish, planting and harvesting the vegetables. We don't spend much time thinking about the nitrifying cycle or ammonia levels. Even if we did, those things are simple to measure and understand. The hardest thing we've found about aquaponics is that so many people are interested in it. We had to start giving regular farm tours every Saturday because we had fifteen to twenty people showing up at odd times during the week to see our farm, and so far over 1,000 people have come on these tours since June, 2008! If you have a Micro System in your backyard, get ready for all the curiosity it's going to arouse!

  4. What is the most important thing to know about the Micro System?

    That it's not about raising fish! Although the fish in your Micro System will attract the most attention, the fish portion of the operation is costly both in terms of consumables and labor, doesn't produce much fish, and CAN't be made to produce more fish without spending more money than the additional fish would be worth. Based on our last two years experience with commercial systems, a Micro System in our climate will produce about 2-3% of its total production weight in fish and about 97-98% of the total production weight in vegetables. The fish part of our operation creates a large percentage of the operating costs, for fish food, electricity for aeration, and labor for feeding, breeding, and harvesting the fish; while bringing in a very small income percentage.

    When you try to grow MORE fish in the temperature range we are farming in (70-76 degrees F), with the fish food costs we have ($0.90/pound), the electricity costs we have ($0.44/KWhour), and the labor costs we have ($12/hour or more), EVEN with the price we're getting for our fish ($5/pound) the more fish we try to grow, the MORE money we LOSE on the fish part of the operation. If you ever hear an aquaponics farmer or "consultant" who tells you you can grow "X" amount of fish in the system they design, you have just heard a completely misleading statement; because the amount of fish you can grow in any system is entirely dependent on the system water temperature (plus MANY other factors they often forget to mention).

    A lot of people selling aquaponics system information or "kits" know how important the fish production is to potential operators, and often vastly over-state the amount of fish it is possible to grow with these systems (they all too often over-emphasize the vegetable production as well), in an attempt to appeal to buyers and sell more stuff. If you hear these kinds of claims, ask the sellers to back them up with phone numbers of real users you can call to verify the claimed "fish production" and "vegetable production". You can't ever get something for nothing, or as a famous author once wrote: "TANSTAAFL!"

  5. What height is the tank outflow fitting (to the hydroponics troughs) installed at?

    The tank outflow fitting should be installed as close to the top of the tank as is possible given the way your particular tank is made. The return water from the pump fills the fish tank up to the level of this outflow fitting, then it flows OUT and back to the troughs. If you put the fitting 8" up from the bottom of the fish tank, the water will only get 8" deep in the fish tank. You are trying to get the maximum depth of water possible in this tank so your fish will feel comfortable and make lots of fertilizer; fish feel nervous in shallow water. Remember to cover the tank with a net so they don't jump out!

  6. What do I put the plants in, what is the potting mix, and how do I sprout them?

    The plants go in 2", 3", or larger diameter net pots. Make a mixture of 60% fine coconut fiber (AKA coir), and 40$ vermiculite (NOT perlite, this is abrasive to the pump and the fish's gills!), soak it with system water, then fill the net pots with it, pack down lightly, and plant your seeds. Net pots, coir, vermiculite, and seeds all can be purchased at garden and nursery supply stores.

    You put the pots with seeds onto a wire mesh table or any flat surface that will drain water off, then water them with a watering can filled with SYSTEM water (that good, nutrient-rich water) so that they stay continually moist (not soaking wet). The seeds don't need any nutrients to germinate, because those needs are supplied by the seed body itself, but as soon as you have a little root and a little leaf, they will benefit from nutrient watering rather than just plain tap water. It may help if you are in a cold climate to construct a little hoop frame over this table and cover it with clear greenhouse plastic; remember to leave gaps at the sides and ends so it can get ventilation and not fry the seeds if it gets warm.

  7. Do I need to move the plants to bigger pots when they get bigger?

    No, you plant most things in 2" pots. Use 3" or larger diameter net pots for things like leeks, tomatoes, okra, and things with big stems. You will notice that the roots of these plants in aquaponic systems are far fewer but much thicker than their soil-grown counterparts. We think this is because of the constant nutrient flow past the roots, which allows them plenty of nutrients without expending energy growing a huge root mass to search for nutrients (as happens in soil).

  8. What kind of fish food do I use, and how much do I feed them?

    Any floating fish food that is around 1/8' diameter pellets, around 30% protein. We use Rangen 3/5 mm floating catfish food.

  9. How do I know when to add iron, calcium carbonate, and potassium carbonate to the system, where do I get them, and why do I need to add them?

    You can get these at garden supply stores, and agricultural supply companies that sell fertilizers and other ag chemicals. The iron is any chelated iron product (may also contain nitrogen, this is OK), and you know that you should add iron to your system when the plants are uniformly yellowing between the veins, old leaves and new leaves both. If you find the old leaves yellowing but NOT the new leaves, that indicates a nitrogen deficiency, which we've never seen in one of these systems in two years of operation. You use calcium and potassium carbonates for adjusting system pH when it gets lower than about 6.4 as indicated by your test strips or pH meter. The calcium carbonate is simply coral sand, ground up very finely like powder (the calcium carbonate you can get that is the rougher consistency of sand does not work as well). Potassium carbonate looks like greyish-white gravel. Mix the calcium carbonate half and half with the potassium carbonate. Add about a half cup of this mixture to a 5-gallon bucket of water, let stand for 1/2 hour, mix well with the water, then dump the whole bucket of mixture into the first trough right where the water flows in from the fish tank.

    Although it's difficult to add too much, only add this one-half cup of potassium/calcium carbonate mixture at a time, then let the system stabilize for a day, then measure pH again. If you find it only went up to 6.7 or so from 6.4, do this addition again, then measure again. If you get your system within the range of pH 6.8 to 7.2, STOP. Depending on your system's conditions, it may take a month to three months until the pH again drops to the point where it needs adjusting.

    The reason you add these three safe, non-toxic, and non-caustic elements to your system is because the only other input to the system is the fish food. Although the fish food has iron, calcium, and potassium in it, the fish use most of these elements for growth. The iron is necessary for the hemoglobin in the fish's blood, which provides the fish the ability to use the oxygen it breathes. The fish use the potassium and calcium from the fish food to make scales, bones, and teeth. As a result, there may be little of these elements left for the plants in the system. When we adjust the PH with these two, they have a second benefit of providing needed calcium and potassium for the plants in the system to use.

  10. Can I put my troughs higher than the fish tank, or put the fish tank higher than the troughs, or do I have to have a single big piece of level ground to build the system on?

    You can build your system with the fish tank higher than the troughs. Just make sure that the fish tank outflow is as near as possible to the top of the tank, as mentioned previously. If you put the tank more than 2 feet higher than the troughs, you should consider getting the next size larger water pump than is specified because you will have a higher head and the originally specified pump will pump a lower volume at the higher head.

    You can also put the troughs higher than the fish tank. If you do this, you need to put the center of the outflow fitting about ten inches up from the bottom of the trough, because this sets the height of water in the trough. Put it at the end of the second trough in the water circuit, because the water will be flowing downhill to the fish tank powered by gravity. You put the water pump fitting in the side of the fish tank about 12" up from the bottom, and pump water UP from the fish tank to the first one of the hydroponics troughs, where you can just lead it in over the top edge of the trough at one end. Either is good, both are great, and if putting either your fish tank or your troughs higher solves a site problem for you, then just remember to follow these instructions when doing so.

  11. Can I feed my fish extra food so they make more "fertilizer", or can I put twice as much fish in the system so that my plants grow faster and bigger?

    No. With the recommended weight of fish in the system it will have plenty of nutrients. If you feed them more than they will eat, this organic material will sink to the bottom of the tank and decay. If you put twice as much fish in the system, you will also generate more decaying organic material. This decaying material turns into ammonia, which turns into nitrites, and then nitrates. If there is more decaying material than all the bacteria in the system can process, it just ends up on the bottom of the troughs and fish tank, where it goes anaerobic and uses up system oxygen. If taken to an extreme, this will stunt, then kill, all your plants and eventually your fish. So you need to just feed your fish what they will eat, no more; and keep the amount of fish in your tank right around 20 pounds.

  12. We have a 2 foot high by 9 foot diameter water tank (which equals to about 950 gallons). Do you think that this can be used with the micro system? Is it too large? I know your book says to use a 150-300 gallon tank, but we wanted to see if we could use what we already have.

    When selecting tanks, fish feel uncomfortable in anything less than 2' water depth (not tank height, they are NOT the same!), and feel best if they have 3 feet depth of water, up to 4' deep maximum. They also need some swimming room; an old 55-gallon drum is NOT enough room to swim, even though it satisfies the depth requirement. You can use virtually anything to hold the fish (and the plants too, for that matter), as long as the material is non-toxic to the fish and plants. Materials that ARE toxic and to be avoided include (but are not limited to): copper, galvanized or zinc-coated anything, polyisocyanate foam rafts (this is usually either pink or white, the only guaranteed raft material we know of is Dow Blue Board), EPDM (a stinky black rubber liner that looks and feels like inner tube material), any kind of treated wood, plywood (it's glued with formaldehyde-based resins, which are TOXIC!), roofing tar and tarpaper, and non-food-grade vinyl liner or material. Some examples of usable (but weird) tanks would be: an old freezer with good enamel inside, with the seams sealed with silicone calk; a fiberglassed plywood box (you better know how to fiberglass or this can turn into a nightmare!); and a big steel tank with the top third cut off with a cutting torch, then the inside painted with three coats of a good food-grade epoxy paint.

  13. I'm in Maine. Do I need to heat an entire greenhouse or would it be enough to heat the water?

    The short answer is "yes", but the easiest firstest thing you can do is to get a cold-water fish if you can find one that's legal in your state. I've enclosed the section from our manual on cold-weather growing just so you can get a feel for the quality of our information:

    II-A-6. Dealing With Climate: Greenhouses, Fish Houses, and Insulation

    A. Greenhouses: How to understand them and select the right one for you.

    v We're lucky to have our farm in a climate that is pretty hospitable year-round. Even so, we are considering putting in greenhouses for our hydroponics next year after the worst winter in 33 years here. For readers who are not farming in Hawaii, or a similar climate, you may need protection for your crops in the winter, and perhaps even most of the year. This means a greenhouse, and perhaps even heating, if you have a cheap source of heat. How do you tell if you need a greenhouse? Ask the other farmers in your area. If they're growing a produce item in greenhouses, you can too, with the added benefits of your produce being organic, and of raising fish in addition to the vegetables. At the very least, you need to keep your fish alive and well through the winter, even if you don't plan on growing produce year-round.

    v Greenhouses come in a confusing variety of types, shapes, materials, and costs. The cheaper ones let less light through and more heat out. The more expensive ones let more light in and less heat out. When you're selecting a greenhouse, you need to strike a balance between the climate conditions you want inside, and what your budget can stand. Your local trusted greenhouse supplier, or a farmer with a lot of experience with greenhouses, is the person you want to talk to about this. Don't just let a salesperson sell you something.

    The cheapest greenhouse is what's known as a cold frame. These are usually semicircular steel frames with plastic sheeting stretched over the frame. They are easy to erect yourself, and relatively easy and cheap to repair if there is wind or hail damage to the structure. A good example of this kind of greenhouse is Conleys CF Series 1000 Cold Frames (Conley Mfg and Sales, 800-377-8441, www.conleys.com on the Web).

    More expensive greenhouses meet Building Code requirements, often have double- or triple-layer insulated plastic sheeting, either rigid or inflated, for insulation, and often have large venting systems for getting rid of summer heat as well as heating systems for keeping temperatures comfortable for the plants in the winter. Good examples are the Conley's 4000, 5000, and 7500 Series greenhouses.

    B. Fish Houses: (Why would fish need a house? They live in tanks!)

    v The first step you take if your climate is too cold is get a cold-water fish to use in your aquaponics. Trout, yellow perch (and some other perch species), some varieties of catfish, and many other fish thrive in a much lower water temperature range than the tilapia we use in Hawaii. How your find out about what's available in your area is to contact the local University Aquaculture Extension Agent or SeaGrant agent (see VI-C-2. State Extension Agents: Agriculture, Aquaculture, State Fish Vet.) . Tilapia need water temperatures between 70-79 degrees to do well. One way you can get the water warmer, if all you have to use is warm-water fish and you are in a cold climate, is to put the fish in a fish house. What's a fish house? Like a greenhouse, but it isn't green, it's black. A simple fish house would be a 2x4 framed structure with black plastic sheeting tacked to three sides and the roof, with clear plastic tacked over the south-facing side (and a door, of course). The fish house will suck in heat and keep it in. This is the cheapest way to get your fish a little warmer.

    v As we've found with our LD systems, you can stop pumping during the dark hours, when the water would lose the most heat back to the environment. So, set your timer to turn off the circulation pump about an hour to half hour before dark, and keep it off until the sun is well up in the morning. Then the heat that has built up in the system water during the day will stay in the fish tank overnight as much as possible. If the fish tank is insulated, then you lose a minimum of heat overnight and the fish stay happy as possible.

    C. Insulation: How to keep what you've gained

    v If you've gone to the trouble of building greenhouses, fish houses, and maybe heating your system water, you want to hang onto what you've paid for (the heat) as much as possible. You do this with insulation. In order of effectiveness compared to cost, we suggest that you first insulate your fish tank. This can be done with 2" raft material floating on top of the tank, and installed under the tank liner when installing the fish tank. You can also put 2" sheet styrofoam outside the tank, cover it with tightly stretched black plastic, and that will insulate the tank nicely.

    v The next thing to insulate is the hydroponics troughs. When you're building them, install a layer of 2" styrofoam under the liner and between the liner sides and the trough sides. IMPORTANT! This will make the troughs 4" wider, and 2" deeper, than the dimensions shown in the construction drawings, so allow for it when constructing troughs.

    v If you're going to buy a greenhouse, you could try installing the fish tank and trough insulation first, and see what kind of heat conservation you get with them alone, before you spend money on a greenhouse. Then you will have some idea how much more heat the greenhouse needs to conserve. You've done the least expensive, most productive insulation first.

    v Here's how we would do it if we were faced with an inclement weather situation, and wanted to save money. We would try the following, in order of effectiveness compared to cost: First, install a minimum of 2" foam insulation on and under the tanks when installing the fish tank and other tanks; THEN build a black plastic fish house around the tanks and stop pumping at night; THEN insulate the hydroponics troughs; THEN buy and install the best greenhouse we could afford; THEN figure out a way to put cheap heat into the water (lots of options here). If we had the time, we would try these options one at a time, testing water temperatures before and after, until we reached our goal. If you can't afford the time, talk to your greenhouse supplier, look at your budget, and make a good guess.

    v Look at it this way: most farmers in temperate climates ONLY have a 5-month to 7-month long growing season. If you can stretch your growing season even by a month or two with the preceding tactics and methods, you will have a competitive advantage over them. If you grow in even a small greenhouse using high-value crops during the worst of the winter, you will have an even bigger competitive advantage.

    I hope this answers some of your questions. It's doable, it's just a combined equation of your budget, your skills level (how much you can build yourself and how much you need to buy), and your business skills. If ANYONE is growing in your area in a greenhouse, then I guarantee you can do better than them with aquaponics, AND get organically certified, which is worth a lot more on the market than conventionally-farmed produce.

  14. How do you grow fresh water prawns in the same system?

    Here's everything we know about growing prawns in an aquaponic system: (also from our commercial training manual)

    Tilapia (or any other fish you try to keep them with) will eat the prawns, so you need to keep the prawns separated from the fish. Everyone likes to eat prawns, even other prawns. To raise prawns commercially, breeders with big ponds stock PL's (post larvae, or juvenile prawns) at 3 to 4 PER SQUARE YARD of pond space, and harvest at 1 to 2 per square yard of pond space. The reason they harvest so many fewer prawns than they stock is that the prawns are territorial and fight with and eat each other. Apparently a lot of the mortalities come from large prawns being eaten by smaller prawns when the larger ones are molting and unable to protect themselves because their shells are quite soft for a long time during the molting process. The only way to successfully raise prawns commercially is to have tens or even hundreds of ACRES of pond space, and even then success is in question because the prawns are susceptible to disease, and predation by fence-hoppers (human thieves).

    The reason we're successful raising prawns is that they are an auxiliary crop to our two main crops of vegetables and fish. The prawns are raised in the hydroponic troughs under the vegetables. We don't feed them anything; they eat the detritus of dead roots and mosquito fish that falls to the bottom of the troughs and seem to thrive on it. We stock 300 +- PL's into a total of 1,024 square feet of hydroponics troughs in a commercial system (a stocking density of 3 per square yard), and 4 months later harvest 50-70 lbs of prawns from that system that sell off the back of the truck for $10/lb in Hawaii. So this would total 150 to 210 lbs of prawns a year from a system that can produce up to 10,500 lbs of organic lettuce and 1,200 lbs of tilapia a year. You can see it is not the largest or even the second largest system output.

    We are experimenting with higher stocking densities and with using substrate inside the troughs to increase the survival rate of the prawns. Substrate is basically wadded-up plastic with a lot of holes in it that the prawns can hide from each other in. We'll put this information up on the website when the experiments are complete. Freshwater prawns have a brackish water phase in their breeding cycle, and because of this, a prawn hatchery is somewhat involved. We figure we can build a basic prawn hatchery for about $1,000 or so, and learn how to run it successfully in two to three months. Because we don't have a prawn hatchery yet, the only way we can obtain prawns is to buy PL's from a local breeder. Most of the commercial breeders have minimum orders of 10,000 or so and high shipping costs, so unless you can find a local prawn breeder that will sell you small amounts, you can't raise prawns easily or affordably. So, don't expect to make a lot of money on prawns or grow a lot of them unless you can solve all these problems, or figure ways around them that no one else has figured out in 50+ years of commercial prawn farming.

    A GREAT source of information on growing prawns can be found at the following downloadable link; this is a reference work on breeding and rearing freshwater prawns at the United Nations Food and Agriculture Organization's website at http://www.fao.org/docrep/005/y4100e/y4100e00.htm#TOC. Look for, then click on "PDF Version" in little blue print at the top right of this document for the downloadable version in PDF format.

  15. What climatic conditions are needed for this to be productive? i.e. at what latitudes will it work, is it suitable in temperate climates?

    Please see the answer to "I'm in Maine" in this same FAQ. It is an explanation of how to do cold-weather aquaponics affordably.

  16. I bought the download of your micro-system, but the lost the download on my computer...how can I get the pdf again?

    We'll just email you if the download failed, or mail you a hard copy if for some reason your download doesn't work.

  17. As for the last question of the size of the tub, are you saying that one may use a larger diameter vessel but must maintain at least 2 to 3 feet in depth? I would like to dress up the fish tub for a more aesthetic look like a backyard koi pond.

    Fish get nervous in shallow water because they can see the predators (us) so much more easily, and they also know they are vulnerable in shallow water. They feel safer, and are less stressed (leading to less disease and fish-related problems) in deeper water up to 48" deep. If you are going for aesthetics, you will still need to come up with a way to shade the tub (to keep from killing the light-sensitive nitrifying bacteria), as the manual explains; as well as some kind of cover or net to keep the fish from jumping out and committing suicide.

  18. I live in PA and am thinking of going into the aquaponics field. You have a great site and i'm planning on coming out to one of your classes. You seem to cover every aspect of this business, but one... Because of the winters here would I need to build a greenhouse and light/heat it using bio-fuels? If so where can I get trusted information in building/maintaining the system to create and use bio-fuels as well as building/maintaining a greenhouse?

    First, thanks for your compliment on the site! Please see "I'm in Maine....." previously answered in this FAQ about cold-weather affordable aquaponics growing. As to the bio-fuel aspect, we are currently building a large biodigester installation under a USDA grant to produce methane to power our diesel electric generator and produce waste heat to heat our residential hot water. The biodigester is a device that produces methane from farm wastes, including animal manure, slaughterhouse waste, vegetable processing waste, and silage. The diesel generator that is run off this methane takes it and turns it into electricity and waste heat as a by product, which can be used to heat greenhouses and fish tank water.

    Because our electricity and propane gas costs for heating water are the highest in the country, we stand to save up to $1,700 per month when we bring this online. We are super excited about the possibilities for cold-climate aquaponics growing this opens up. The biggest barrier to growing through the colder months in a temperate climate is the cost of heating your greenhouses, which is not cheap even where energy is cheap. The waste heat from the diesel generator neatly solves this problem. We WISH there was already "trusted information" as you ask for, on building and maintaining such a system; we'd be doing that instead of developing it ourselves! Unfortunately, the cost of the "small" systems for which there's "trusted information" on construction and operation start at around $500,000. That's why we're developing this; we expect to have plans available in about a year for a range of systems of different capacities costing from $5,000 up to $50,000.

  19. Do you have an automated system, if someone is not present to feed the fish every day?

    We've found out that automated systems are not a good idea because they make you think you can ignore them. You come out a few days later when you remember, and you've got dead fish or plants, or both. This doesn't happen very often when you are paying attention, because these systems are largely self-balancing, but they DO need the farmer's shadow (they need you to PAY attention to them, just like anything else living does!). That said, you can skip feeding the fish for up to 2 weeks easily without killing them, in the case of tilapia.

  20. Why can't I have the grow beds raised up at waist level so I don't have to bend for gardening. The pictures you have shown are at ground level . Can the grow beds be raised to waist level and the fish tank placed beneath it ?

    There's no reason you can't raise these beds to waist level, if you don't mind the expense and nuisance of having to build a structure that can hold a ton of water for each grow bed. You can do it, but it will probably add $3-400 and quite a bit of labor to the cost of a 64-square-foot Micro System, and much more to the larger systems. Also, we don't plant into or harvest out of the beds themselves, so there's no bending over. Because the vegetables are on light and easily-moved foam rafts, you simply take a raft out and put it on two sawhorses to either harvest from that raft or plant into it.

  21. Where can the recommended 150-gallon Rubbermaid or Behlen fish tank be obtained?

    At farm and ranch stores, and often at feed and grain stores. These are places that sell stuff to farmers and ranchers, and are often NOT real visible from the road because all the farmers and ranchers know where they are. Look in the phone book.

  22. I'm ready for system startup only one problem. I don't know when I'm going to get my fish. Should I go ahead and do the startup or should I wait until I know when I'm going to get the fish? Thanks!

    Go ahead and do the startup if you think you'll get the fish within the next month or so. You can use all kinds of fish: tilapia, mosquito fish, carp, smallmouth or largemouth bass, catfish, koi (Japanese ornamental carp), so don't get fixated on a particular species or even SIZE of fish. You eventually want about 20 pounds of fish in the system, but you can start out with 10 pounds; this can be 2,000 mosquito fish, because they eat fish food and poop just as well as any other fish do!

  23. Is there a way to use the micro system indoors with grow lights?

    Yes, we suggest you use 48-inch double lights with T8 or T12 bulbs (the T8's are more energy-efficient!). Get bulbs that have a 6500 Kelvin color temperature (all flourescent bulbs have a color temperature listed on the box). BARELY ENOUGH light would be two 48-inch double lights over each 4' by 8' trough, GOOD light would be three 48-inch double lights over each 4' by 8' trough, and EXCELLENT light would be four 48-inch double lights over each 4' by 8' trough. Take a look at what electricity costs in your area, get out your calculator, multiply the total wattage of your lights by 24 hours, then by 31 days, then by what your electric utility charges for juice, and you'll know how much you'll spend to light your system.

  24. I have an interested friend who has a very large steel tank cut lenghtwise with a half moon shape that currently holds rain water runoff. Can he weld in a divider so one half can grow fish and the other veggies?

    You need approximately 20 times the area in grow beds that you have in fish tank. If you put the divider in 1-20th of the distance from one end to the other, it would work (other than the cost of welding and painting a steel tank so it doesn't rust out).

  25. Do you mix fish of different ages in the one tank, in order to have rolling fish harvests and a more stable nutrient supply? If so, does some portion of the small fish population get killed/eaten by the bigger fish? Or do you simply raise one batch of fish at a time?

    Yes, we have fish (tilapia) from one inch up to two pounds in the same tank and harvest only the largest ones when it is time to harvest; this is called CMSGH (Continuous Mixed Stocking/Graded Harvesting) and is the way to get the most production out of a single tank. What you want to avoid is having two-inchers and half-inch-long fish in the same tank, the two-inchers will eat the smaller ones. Once they're larger than 2-3" there don't seem to be cannibalism problems.

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