• Confessions of an Aquaholic - The Past Year in Review (A Reflection)

    Aquaponics is an addiction and I get my daily fix every time I harvest a tomato, cucumber, head of lettuce, or catch out a full grown trout. I haven't found a cure (nor am I looking for one). I suppose crop failures, fish deaths, bug infestations or job relocations could prove fatal.

    This month marks the one year anniversary of my addiction and I reflect back on the disasters averted and lessons learned.

    System Sizing

    My 250-275 gallon IBC Tote fish tank (1000 liter) will easily support 500 gallons (2000 liters) of grow beds and a 4' x 8' (1200 x 2400mm) floating raft tank. I started with 2 grow beds and the raft tank. Now that the fish are much bigger, more grow beds are needed, especially in the winter when the light levels are low and plant growth (nitrate uptake) is slowed. The ration of 1:2 fish tank to grow bed volume is easily supported.

    Gravel Size

    Expanded Shale Aquaponic GravelThe 3/8" expanded shale is to small for the gravel beds. The water is slow to move through it and the solid wastes build up on the surface, although none leave the bed. Every other week I wash the solids down into the bed where the worms can work on it and to break it up. When I install additional beds I'm trying 2 things: 1) I'll use the 3/8" Shale around the Bell Siphon standpipe as I like the filtration it provides, and 2) I'll use 3/4" shale or expanded clay everywhere else. This should let the water flow easily throughout the bed, while still filtering out all the solids, moving the solids into the bottom of the bed where the worms can work on it.

    Floating Raft Tanks - System Configuration

    In my system, the fish tank overflows into the grow beds AND into the raft tank. When the fish were small this was not a problem. As the fish grew, and their solids output grew, 2 things happened: 1) the water became cloudy as the water going through the raft was not getting filtered, and 2) the roots of the lettuce became clogged with solids, inhibiting growth and making a mess. When the fish were little, a bi-monthly rinsing of the roots was sufficient to keep the roots clean and clear. Now I have nylon stockings over the inlets to screen out the solids. These have to be manually removed and cleaned twice daily. While cleaning them is not difficult, having to clean them ties me to the system night and day. Furthermore, my lettuce takes 25%-50% longer than it should to mature. Reading more of Dr. Rakocy's research, he found that the first few rafts in the UVI system were slower to grow, until they added filtration and degassing tanks.

    When I add the additional gravel beds, I will direct all the fish tank water through the gravel beds. This will filter the water and remove the solids. Then the water flows out to the sump tank, where it is heavily aerated before returning to the fish tank. I will add a bypass line in the return line and route a portion of the sump water into the raft tank. This way the raft tank only gets filtered, degassed water. This also eliminates the need to clean nylons twice daily, creating a more hobby friendly system.

    System Balance - Fish Load

    While ultimately the amount of fish a system will support corresponds to the amount of feed fed daily and the systems ability to convert and use the solids and nitrates that are output, we tend to push the limits, seeking the 1/2lb of fish at harvest per gallon of fish tank water or 60 grams per liter. After all this is the loading for the UVI system, and if they can do it, we should be able to as well.

    Unfortunately, this is misleading and the lower levels recommended by Murray Hallam and others are more realistic. I carefully calculated the various feed rates and harvest sized for the fish in my system and stocked the tank to its maximum capacity; 100 bluegill, 75 hybrid striped bass, and 50 rainbow trout. Assuming 3 per gallon for bluegill, .5 per gallon for bass and trout thatís 283 gallons of fish tank needed. The first 6 months it worked. Then dissolved oxygen levels began dropping, water began clouding and nitrates began climbing and I had fish not looking so good

    I've since doubled my aeration, doubled the water flow through the fish tank and resorted to 10% water exchanges almost daily. I recommend going with 1/2 the amount of fish I mentioned. Even the UVI system actually runs at 1/2 the recommended level and here is why.

    In the UVI system they have 4 fish tanks that share the same water. The tanks are stocked in rotation every 6 weeks. When one tank is ready to harvest at 24 weeks, one tank has fingerlings 6 weeks old (1/4 load), one tank will be at 12 weeks (1/2 load), another at 18 weeks (3/4 load). In other words, if you average those out, at harvest they are only at 50-60% of the 1/2lb fish per gallon of tank overall as the system never reaches the maximum loading at the same time. I'm cutting my stocking levels in half for the future.

    Water Heating

    My method of heating water with a residential water heater and a temperature control hooked to a sprinkler valve works, but I'm not happy with how much it restricts the water flow and requires an oversized pump to force the water through the water heater. I may look at using the water heater to heat water that flows through hydronic heat tubes under the raft tank and looped in the sump and/or fish tank as an alternative. The water heater is inexpensive to operate (compared to electrically heated alternatives) but I think there is a better way.

    Plants and Bugs

    Aquaponic Grown Cabbage Head
    Aphids are my nemesis. I'm now on a regular schedule of beneficial insects (monthly). I even get aphids on many varieties of lettuce and they love the tomato plants. The beneficial keep them under control as long as I bring them in regularly.

    European Cucumber ClusterI've had excellent results with Roma tomatoes and European seedless cucumbers. The cucumbers are sensitive to low potassium levels and powdery mildew, but have been solid performers in my system. The tomatoes are susceptible to low levels calcium, but now that the system is mature, they just flourish. Bell peppers have also done well, but are equally susceptible to aphids and white flies. All three of these take 2-3 months before they start producing. Once they start, you get 9-12 months of continuous production before they need replaced. Peas and beans also grew well, but seem to attract more bugs in the greenhouse than I like. Cabbage grows well and is relatively bug free, but takes a long time to mature. Lettuce is a quick harvest and most varieties are bug free.


    We had our first harvest and the verdict is in, more rainbow trout, less bluegill and bass. The bluegill were stocked as fingerlings in April, the Hybrid Stripped Bass as fingerlings in July and the rainbow trout as 4-5" fish in October. The rainbow trout are 1/2-3/4 lb (225-350grams) and eating size in just 4 months. The HSB are 5-6" and only ľ-1/3lb (150-200 grams) after 7 months. The bluegill are 2-3" and 50-80 grams after 10 months. The rainbows are the best eating and yield the most meat per pound. The bass also taste great and yield almost as much as the trout. The bluegills are boney, thick skinned and difficult to skin and handle, although tasty, however the bluegill are indestructible, while the Bass are ultra sensitive, with the trout somewhere in between.

    First Aquaponic Fish Harvest
    My concern with trout was the water temperatures. Initially I stocked the trout in the fall and let the system stay down around 65 degrees (18C). The trout did well but the tomatoes and peppers completely stopped growing or setting new fruit. I raised the temperature up to 68 degrees (20C) and the tomatoes and peppers are growing and setting fruit again and the trout continue to grow. My goals for the coming year are to keep as many trout as I can for a longer period of time, with a few bass for the hot summer months. I would like to have tilapia, but regulations prevent that. I can get trout in almost any size most of the year; they grow fast and taste great. It will only be in the mid summer heat that the temperatures will be too high.

    Iím sure mixing 3 different species has affected the growth of all three and the more aggressive trout and bass, keep the bluegill from coming to the surface and eating well. Ideally I would only have 1 species at a time, or have multiple smaller tanks and keep them separated. At most I will have 2 species in the future.

    The Future

    This addiction of mine requires a larger and larger dose of aquaponics as time goes by. This year I hope to attend the UVI Seminar, add a remote monitoring system, including a tank camera, and look at a smaller 4 tank staggered production system that is 100% floating raft.
    Comments 1 Comment
    1. nwestwood's Avatar
      Gravel size - my solids build up was not due to the small gravel size, but to having to many fish. Keep the fish in balance and solids are not a problem. I added expanded clay to sections of my gravel beds, they plugged up just a fast, until I reduced the fish load. If I could get screened expanded shale in 1/2-3/4 size I would do that, but the 3/8's worked well under correct fish densities.