Tilapia pond setup, a few questions...

Delilah

A few years ago we built this 700 gallon pond with a pump and a stream. The plan was to put 2 or 3 goldfish in it but that never happened and it basically turned into a smelly, dirty, stagnant puddle of water. So anyway, after a few months of reading about aquaponics, we decided to connect this with a grow bed and raise some fish in it. I was hoping to raise fish that are native to our area such as yellow perch and channel catfish and have them shipped through the mail from a fish hatchery. Unfortunately by the time we finished setting this up it was too hot to ship those fish, so instead we bought 25, 1 lb. tilapia. Now the plan is to keep the tilapia until fall when they will or will already have been harvested and then order some catfish and yellow perch (maybe bluegill too) and raise those year round.
so here was our pond last fall

and here it is now

700 gallons of water for the fish

150 gallon rubber maid stock tank as the grow bed filled with gravel and a little hydroton on top

this is the stream that leads the water back to the pond which is an additional 20 (more or less) gallons of filtration

the tilapia seem to be doing well

so there are 25 tilapia (each 1 pound), 1 feeder goldfish (we started with 15 but moved the rest to their own tank) and one mystery fish who is black and about an 2" long who was thrown in with the tilapia.
the oxygen is usually 5 ppm during the day after adding the tilapia (was at 10 with 15 goldfish). Is this enough for the fish or should i add more aeration? the only water movement is from the water going in and out of the grow bed and if I needed to I could add a fountain.
After adding the tilapia (that was 2 days ago), the nitrite level has gone from 0 to .5 while the nitrates stayed the same. I had the system cycle for a month with some feeder goldfish before adding the tilapia. Is a nitrite spike to be expected after adding the fish, or does this mean I have added too many fish? If there are too many fish how many would you recommend I take out?
All the systems ive looked at have the water go into the grow bed and come out the bottom. We wanted to partly cover the stock tank with dirt so we have the water coming in a few inches bellow the surface and coming out a hole in the top. the good thing is there is no water fluctuation in the fish water but im concerned wether this will provide enough water circulation in the grow bed?
So if there is any advise you have or something I should change I would love to hear it

keith

with a 150gal growbed, you're pretty close to maximum stocking level that is recommended..
the water level in your gb looks to be a little high, you want it to come to about an inch or so under the surface, with it coming over the surface you can get some algae problems.
add a few more growbeds.. looks great so far!

chillidude

Yes, the spike is to be expected as you've increased the biomass significantly.

You are pushing your stocking level to the limit so you are going to continue to get spikes. If it is at all possible, get another growbed in there somewhere to provide more biofiltration, soon.

Delilah

Id rather just decrease the fish load rather than adding more grow bed. This is probably more fish than we have ever eaten so I don't mind having a lower stocking level. How many fish or pounds of fish would you recommend for this system with 170 gallons of filtration (thats the tank + the stream)?

chillidude

Apologies - that didn't come out quite right.

What I meant was you're pushing the system by suddenly increasing the biomass that much. The system will adjust, though I wouldn't put any more fish in there until you've eaten some of the ones that are already there.

Hold back on the feed until you don't show anymore nitrites.

Stocking wise you're at about the right ratio of fish mass to biofilter, and it should cope with further growth.

Your DO levels are fine for tilapia, and probably for the yellow perch, but I don't know enough about bluegill and channel cats to comment on them.

keith

with 170 gallons of filtration, max stocking density would be around 42lbs, but that would really be pushing it.. having the extra water should help though..

keith

with 170 gallons of filtration, max stocking density would be around 42lbs, but that would really be pushing it.. having the extra water should help though..

oh, and bluegill are pretty tough,, and will grow to 1lb in a year if you have a good quality feed..
yellow perch don't like the water getting to warm, if your water hits the 90's they will be stressing

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