mikecoen

20 fish, 800 gallons of water, no nitrates

6 posts in this topic

I was so thrilled with last winter's small experiment with two IBC, 60 small tilapia and 30 square feet of grow beds that I took a big jump, built a 20x40 insulated building and maybe the jump was too big because I don't have any nitrates yet.  I have the two IBC, 20 small fish, two small sumps with fiber media in series (20 gallons each) with no grow beds but six 4x8 foot rafts, each with about 60 gallons of water.  I just added 15 square feet of media/growbed.  All I have growing in the first of the 6 rafts is about 50 lettuce seedlings.  They aren't growing.  Ammonia is about .8, nitrite 0, nitrate 20, pH 7.5, temperature 80F, lots of aeration.

Any ideas?  I thought I might isolate the one IBC to circulate with the new gravel growbed, add household ammonium and see if I can encourage bacteria to get to work for me.  The gravel bed sits atop that IBC and is flood and drain. I can keep the rest of the system from getting any of the enriched/ammoniated water until I see if it begins to cycle with the addition of the growbed gravel.  There are no fish in that IBC; they are all in the other IBC and either or both feed back to the sumps with a solids lifting overflow.

Is the problem that I have such a huge ratio of water to the number of small fish? 

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How long has it been running?  How long have the lettuce been in their rafts?  I'm not really the fish guy around here, as everyone knows, but it seems like a pretty light load to be trying to grow much yet. As far as your lettuce are concerned, I'd recommend a capful of Maxicrop (or other liquid seaweed fertilizer) every few days. With that much water, even every other day would be ok. It's not cheating and buys some time while your nutrient load builds up.

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The system has been in this state for about two months.  The lettuce raft (the other 4x8's are just water with floating styrofoam covering them) has been getting a little fertilization for the past week and everything looks better that way.  I am going to add ammonia to the IBC that has no fish and isolate it to just recirculate, flood and drain, with the 15 square feet of gravel media about 9 inches deep.  That way I won't shock any other parts of the system and can monitor and confirm that I am getting nitrate production.  I guess I'll gradually let that tank blend into the sumps, growbed and the other IBC that has the fish.  I do want to add more fish when I can find some locally again, or even put a different kind of fish in the extra tank.  I'll post again when I learn something, meanwhile thanks for the helpful input and opportunity to meet others in aquaponics.  

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What are your temps (water and air), and are you using lighting or going all off sunlight? Slow growth could be due to either low temp's and/or insufficient lighting this time of the year. I would be hesitant to add ammonia, and instead give the system a bit more time.

 

Sorry - just noticed that you have high temp's and additional lighting... lack of sleep really does make one dopey.

Edited by edmolina (see edit history)

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the air temp I had not mentioned - it gets up to 80 due to the passive solar effects of the building and down to 60 or even 50 when we have very cold weather and/or clouds that limit the active solar thermal gain.  The grow media of course stays warmer, like the water right below in the IBC which circulates in flood and drain fashion every hour for 15 minutes.  I did put ammonia in that tank and shut some valves so there are 200 gallons of water and 15 square feet of pea gravel, 9 inches deep.  I'll check ammonia levels tomorrow and watch nitrites to see if they spike.  Thanks all for the thoughts and ideas.

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I have given it a week, isolating 200 gallons of fishless water and a gravel bed made of the top 10 inches of the IBC.  The pH was 8 so I buffered it down and it went a bit low, now is 6.4.  I used too much ammonium to kick start it so that is still way high.  The nitrites are 5.0 and the nitrates are between 50 and 80.  When the ammonia and nitrites get low I will open this part of the system back up again to the other tank with fish and the two small sumps and the 6 large (4x8) rafts.  I did add an organic plant food to the one raft where I have lettuce starts.  They immediately greened up so I was just low on nutrients and that's why the lettuce was sitting on idle.  Air temp in the grow building fluctuates between 50 and 80 with the norm being about 70.  The water temp for the fish is 80, the 200 gallon IBC without fish is between 70and 75 degrees.  The rafts are about 70 degrees.  This is an increase in the nitrites and nitrates so I am beginning to cycle.

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