System 4
In late october it started to get too cold for tilapia outdoors. I harvested all of the fish from the apartment system. They ranged from 1.25-1.75 lbs. I have only about 100 tilpaia left from all the fry I spawned. I chose some due to fast growth, some due to color and some randomly. The others were usually grown to minnow size and released into my main system as "a treat".
The next system is an garage system designed only to keep my tilapia alive over the winter. It's not designed to run permanently or year round. I did water changes with my outdoor system every couple of weeks to keep nitrates down.
I didnt use any insulation because I knew this would only be a one winter thing and then I would be moving, again. I was able to make the winter without any deaths using 1kw of aquarium heating elements. It wasnt enough heat to maintain 70 degrees but it would keep the water "high enough". I didnt run the heaters constantly, only when it started to get too cold.
Hind sight it would have been nice if i had a day to day chart of the water temperatures but I did not do that.
In texas, most winter days are around 60 degrees. We get cold fronts that come through and freeze but they usually only last a few days. The water temperature did get into the mid 40's at least once, but for no longer than a 24 hour period. Since mozambique tilapia are supposed to be be mortal at 55 degrees, i thought this was interesting information and worth sharing.
a compact system, The fish tank overflows into two 55 gallon barrels which are full of expanded shale. The "filters" emptied out of the bottom and gravity pushes the water into the 55 gallon barrel sump. A pump lifts the water from the sump in to the "grow bed" which has no substrate and only grows duckweed under a $10 T8 shop light w/ 1 "daylight" and 1 "sunlight" bulb to provide spectrum. The "grow bed" overflowed back into the tank.
I am keeping 3-4 dozen 3-6" tilapia in the IBC tote and countless smaller 0-2" fingerlings in the sump tank.
red wigglers (placed intentionally) and snails (not so intentionally) helped break down solids and uneaten food particles.
Drain out the bottom to try to avoid anaerobic zones.
sump with 600 gph ecoplus. It probably only got 300 gph at the 4 ft head height.
Tilapia do eat duckweed but in this case i am not growing it to feed. I remove the duckweed whenever I can to remove nitrates from the system. You may see chunks of pvc in the "growbed" and those are for hides, i started experimenting with raising marbled crayfish (Marmorkrebs) with the intention to try them as a supplemental fish food source.
Often new people to aquaponics believe they can grow a bunch of duckweed and not need to buy fish food. Duckweed is high in omega-3 and high in protein. It is a good supplement. But keep in mind that the actual plant is 98% water so it take a LOT of duckweed to GROW a fish. I believe it may be possible to go off commercial feed with a diverse food strategy that includes duckweed but never with duckweed alone. I have seen people say on forums that too much duckweed makes the tilapia taste like duckweed. I cannot confirm/deny that statement and have no plans to try.
brian
