Daily, Weekly, And Monthly Tasks In A Commercial Aquaponics System
Feed The Fish:
The fish food we use is Rangen 1/8” floating catfish food. You can use any floating food that has about a 30% protein, 6% or more fat content, but TRY to find a fish food that comes in the nice small 1/8” pellet size, as we have noticed problems, both with acceptance by the fish when they were fed larger sized pellets, and with the growth rate and health of the aquaponics system. Feed your fish three times daily, morning, noon, and 1 hour or so before dusk. Feed ad libitum, which means as much as they will eat. When you first feed a group of new fish, start feeding a little bit at a time until you are sure how much the fish will eat. Check back in 15 minutes after feeding to see if the feed is all gone, if it isn’t, it means you need to feed them a little less next time. If they eat it all in 5 minutes, you need to feed them a little more next time.
Water Testing, Measurements, And Recordkeeping:
When we began this adventure, we were nervous and inexperienced and checked water quality twice a day. We ended up with a simple form to fill in when feeding the fish in the morning (below). We check ammonia, dissolved oxygen, and nitrites/nitrates two or three times a month now, and this is useful information. If you are observant, it is immediately obvious if something changes or is wrong. The best thing about keeping records is that you can look back and correlate some event in the vegetables with some event that happened with the fish and be able to tune your system to get desirable events to happen more often, and undesirable ones not to happen at all. We can tell what’s happening now by just looking at and sniffing the water (Tim drinks it!), and we still do record keeping, but we are far more relaxed about it. Our record form looks like this:
Daily Check List Date:_______Time of Day:__________
System DO Temp pH Ammonia NO2/NO3 Feed Morning
Breeding Tank 1
Breeding Tank 2
Check mesh screens in fish tanks: 1 2 3
After 1/2 hour, check for uneaten feed in:
#1 #2 #3 Breeding Tank 1 Breeding Tank 2
You know the quantity of vegetables you harvest; weigh your fish harvests so you know how many pounds of fish you are growing as well. Keep track of how much fish food you go through; by comparing this with your fish sales in pounds you will know your feed conversion ratio, or how much food over the life of a fish it takes to make one pound of fish. Why is this useful? If you notice your feed conversion ratio is 5.4, when you know it should be around 1.7 for tilapia, you know you need to find out where your feed is disappearing.
Keep good records. If you go to a bank or even a relative for a loan, they will want to see complete, impeccably kept records as part of your application. Well-kept records also keep the IRS from assuming the worst and making you pay for it if there is ever a question about your taxes.
Check all filters in the system with a casual eyeball whenever you pass by. Filters or screens will flow just fine then clog and overflow in what seems like a very short time. A plastic bag blows in on the wind, someone drops a couple of net pots full of coconut fiber in a tank accidentally and it winds up on the filter. A sure sign that something needs cleaning is when you see water coming down the hill from the aquaponics!
Harvesting Fish/Restocking/Carrying Capacity of System
We harvest when people call and come to the farm for fish. This is easy because we don’t have to deliver or spend time selling off the farm. You can harvest the fish as often as you want as long as you don’t over-harvest and cut off your fertilizer supply (we don’t know how low this is; we are pretty certain it is a lot lower than the 0.3 lbs. of fish per square foot of raft which works well in our LD systems). We estimate how much fish is in the tank and try not to let the total weight of fish in a 1,024 square foot system get less than 200 lbs. or over 800 lbs. Remember: you can always feed 800 pound of fish the same amount of food you feed 300 pounds of fish to keep your ammonia down!
We use a simple fish size-grader made of PVC or a net to crowd the fish into one part of the tank, then scoop-net out what we want. We try to get the bigger fish because they grow slower and eat more food than the smaller fish per pound of weight they put on. If we harvest 10 fish, we restock with 11 smaller fish (at least 2-1/2″ long) to replace the fish we harvested plus 10% to account for any mortality.
We harvest and pack our vegetables two days a week, pretty much an 8-hour day each time for about 5,000 square feet of system; this takes four people each day. Then we replant, which includes seeding the new net pots, putting them into the sprouting tables, and taking the more mature seedlings in net pots from the sprouting tables and transferring them to the rafts. This takes two people about four hours each day, two days a week.
You can sometimes raise the level of nitrates in your system by feeding the fish more, up to a certain point: you can get nitrates up to 5 to 10 ppm with some additional fish/feeding, but if you try to raise them more than that, the only thing that increases is your ammonia level. If you continue overfeeding in an attempt to raise the nitrate level, the nitrate level will simply stay the same, while the ammonia level will increase to the point that it inhibits the nitrifying bacteria, and you will actually see a decrease in both nitrite and nitrate levels. Stop feeding the fish so darn much!
We don’t know (no one knows; at least not yet) the minimum levels of nutrients on which these systems will function adequately, nor for how long. All our systems have operated on the same extremely low levels of nutrients (0 to 3 ppm nitrates, consistently) in a stable manner for so long that we no longer worry about them. If your vegetables are growing well, don’t worry about what the nitrate level is.
Monthly Or Longer (But Sometimes Shorter)
After four and a half years of operation of our commercial systems, we finally had a blower motor that needs a new capacitor. Our ice machine and refrigeration (walk-in refrigerator) has needed maintenance a couple of times in the six years we’ve been in operation. We have some corrugated galvanized steel fish tanks with the 25-mil food-grade vinyl liner; the liner developed small holes from small children whacking it with sharp objects after three years. Partially draining the tank and putting “Gorilla Tape” over the holes fixed this. Other than that, we haven’t had an equipment breakdown, and all troughs and fish tanks are holding up well.
In smaller systems such as the Family System and MicroSystem, what will fail is the water pump and air pumps. They don’t give you lots of warning, they simply quit. It’s a good idea to check your system with a walk-around twice a day to make sure the water and air are both flowing, and to have a spare air pump and water pump available. If you really want to do it right, install the spare air pump onto the airline, but don’t turn it on until the first one breaks. Then get another spare right away!
We also noticed signs of dry rot on the outsides of two first-generation plywood-epoxy-fiberglass tanks that we DIDN’T coat with HiBor water-based wood preservative before painting (after six years of operation); we removed and replaced those sides. We now use three coats of a good oil-based paint on top of the borate-based wood preservative when we build plywood/fiberglass tanks, and have recommended this in our manuals since 2009.