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I have a 150 gallon tank that has been established for over three months now, with 24 hybrid bluegill. I had to reduce the temp by 2° over several days. From 75 to 73 degrees F. I did this because I felt my lettuce was bolting, as It was growing tall, but no flowering. Anyways, my gills have slowed down their eating, and some seem to have stopped all together. There is plenty of airation. PH is fine. Ammonia, and Nitrite are zero, but nitrates are at, or above 160ppm, which is where its been for two months. There does seem to be some territorial disputes among the larger ones however, but not sure thats the problem. I should just turn the temp back to 75°, but I don't believe thats the issue, just coincidence. I did supplement their food with premium talapia grouth pellets, along with their normal premium fingerling pellets from The AP Source. Anybody have any input on this phenomenom?

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Give your fish a few more days.  The neat thing about fish is they can go a long time without food before they kick the bucket.

It may be that they just need a few days to adjust.  My tank will move between 76 and 73 and I only feed my fish every other day.  They are growing and doing well. (Tripled in size sind late August in a 300 gal tank)  Sometimes we seem to get excited over things and maybe we should just sit back and not try to push too hard.  Just my thoughts.

Hey, sorry this is a little off topic, but you mentioned your lettuce seems to be bolting. Are you using artificial lighting? I found that turning my lights on too long caused my greens to bolt right away. I think its actually the light instead of the temperature that causes bolting, although it could be a combination of both.

You may want to understand what your nitrate levels are by getting them into a testable range again. Is 160ppm or above, 180? 500? 1000? Nitrates arnt that harmful to fish but they can be if they are too high and not eating could be a good indication that this is getting to be a problem. There is likely a good reason the aquarium test scale ends at 160. To me it says your "aquarium" or in this case aquaponics system should not be outside this range. I believe most freshwater aquaculture systems try and maintain under 80ppm but it was awhile ago when i read that figure. I believe larger healthy aquaponics systems are running very low nitrate levels and Ive read many times peoples plants are growing just fine with a nitrate reading of 0 (they use up the nitrates as they are detectable). Do you need to maintain your nitrates at 0? No but my point is getting them under 160 so you can monitor them would be a good idea. 

There are experienced folks here with better advice then me, but several smaller water changes (maybe 30% every other day) would be the best way to go than doing something drastic. The sudden drop in high nitrates could stress/kill the fish so better to drop it over many days until its in a readable change again vs doing it all at once.

These replies all seem to make good sense, so I am going to take the advice given. It sure won't hurt.

Dont forget you can water the dirt garden and house plants with the high nitrate water too :) 

Three 30% water changes and nitrates are still off the charts. Fish are still skitish, and not eating pelleted food. I throw a few redworms in, and they are like piranah! At least the small ones are. The larger ones just gaurd their corners? I was in the process of setting up a couple raft trays with new plants well started, when my sump tank pump went out. Thank god I added in an overflow pipe, or it would have drained my system! I can only utilize the nitrate rich water on my house plants and seedlings, as there is still several inches of snow here. I did raise up my lights, but can't pull the bolted lettuce until I get the rafts going, or my nitrates will rise even more. A new pump tomorrow, and another 30% water change and we'll see if that helps. I may also bring my temps back to 75° after seeing if the water change made any difference, or I'll never know what worked if doing it all at once. Thinking I might have put the gills in spawn mode by lowering it in the first place?

Im out of suggestions at this point. Hopefully one of seasoned experts see this and respond with something better. Good luck anyway and keep the thread updated. More change of it getting seen that way.

How is your water movement? Are the fish provided hiding/nesting areas? Approx fish size? Light levels in the fish tank? Air temp?  

These are all things that could cause a change in their eating habits. Having a nitrate problem makes me a little concerned. What are you using for your water changes(municipal tap, well, pond, filtered, RO/DI)?

I have two large air stones moving the water 24/7, on top of the flood and drain cycle every 15 minutes. The larger fish are aprox. 4 inches, with some 3 to 2-1/2 inchers mixed in. I have the tank covered with 3/4" foam most of the time, and I remove this 15 minutes to 1/2 hour before feeding to allow them time to adjust to the light.

   I use municipal water that is aireated in a 55 gallon drum for 48 hours, and PH adjusted. I am trying to correct the nitrate level, as it probably is the culprit. They do appeared to be quite stressed. The city water has no violations, and is the cleanest in the state, coming from Lake Michigan. It has an average flouride content of .7ppm.

I know when I had a reef tank, using municipal water (even aged) could lead to nutrient issues, including excess nitrate/nitrite levels.

In the AP system, there is the unique issue of needing nutrients and minerals for our plants, yet still providing very high quality water for our fish.

I would suggest trying another water source (known clean well system with newer plumbing, filtered water) for some water changes to see if that can help regulate levels.

if you're using floating pellets, try this.. get a zip type baggie, put 1/4 cup or so of pellets, and about 1/8 cup water, seal and refridgerate overnight, turn a couple times to make sure all the water gets aborbed... when you're ready to feed the fish,,, cut a worm or two up into smaller bites and put some wet pellets in at the same time.. the pellets will sink slowlly if you give them a light squeeze...

after they are taking the wet/sinking pellets, add a few dry pellets when you feed.. gradually change the ratio of wet/dry till you are just feeding dry pellets..

 then you only feed worms as treats and the fish should stick to the pellets

Funny you mention the water, and worm mix with the pellets Keith. Aside from refrigerating, this is exactly how I first started the fingerlings into eating, when I first got them. It worked well, and I'll try it again. Thanks!

   As for the water. Like I said. Its the cleanest in the state of Wisconsin. But that doesn't mean there isn't contamination in the pipes running through town. Its just that they (fish) were so healthy, and active for three months that I'm still thinking nitrates like Chris mentioned above. I will try the hard well water in a future change though. I have to drive 20 miles to get away from this huge layer of limestone found around Lake Michigan, and Superior. Besides it is still in the teens and twenties her so I probably pull into the driveway with a drum of ice. I did get my raft trays set up, and need to get

   foam board for planting. It is now a hybrid system!

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