My Large blue tilapia are dying

[harryarmst]

I am having a problem with my large, eating size, tilapia in my 400 gallon aquaponics system. The PH is around 6.8, the ammonia is at 0.5, the nitrites are at 0 and the nitrates around 30-50. The fish get lethargic, then their eyes start to turn white and a few days later they are lying at the bottom of tank. Any ideas?

Thanks,
Harry - Orlando

[kellenw]

Hi Harry,

Your smaller tilapia are doing fine?

[harryarmst]

No actually some of the smaller ones have died the same way as well. I have a 75 gallon tank in the house with about 40 2-4" ones that are doing fine. The outside large tank was being replenished with rain water but the rain water was ph 6 or below so I was compensating with horticultural lime. Just this week I gave up on the rain water and am now replenishing with tap water. They were fine all of last year with the tap water.

Harry

[saguarotreker]

You might want to determine if there were any changes to the city water system while you've been using rain water.

[kenjivaj]

Did you do something like this? Hope this answer solve your problem.
http://freshaquarium.about.com/od/wa...changekill.htm

[harryarmst]

Thanks for the responses. I have not done a whole water change, I just top off the system when the sump tank gets low. Until last week I had been using rain water but have been having the fish problems for 2 or 3 months now. The main tank is 400 gallons, the sump tank is about 180 gallons and the grow beds are 120 gallon tanks cut down the middle and filled with gravel. there are eight 1/2 tanks so about 480 gallons worth of gravel beds. Last year I had to move half the tanks so they got emptied and rinsed out, I am wondering if they need to be cleaned out again. I understand the need for the beneficial bacteria on the gravel but I feel I should shovel the gravel out and rinse the grow beds out. I only have about 8 or 10 fish left in the system. I am getting ready for my fall planting and the few tomato plants left are on their last legs.

Harry

[kellenw]

If you are just topping off rather than doing a significant water change, I don't think I'd be too concerned whether it came from tap or from rain. I doubt that is the issue.

Have water temperatures been swinging widely? Do they spray for mosquitoes regularly in your area?

You might also try dissecting one of the dead fish to see if there are any parasites or organ issues.

[Damon]

i noticed that you didnt mention a disolved oxygen level in the run down of your systems stats. increasing the number of fish will decrease the available levels of DO in the tanks.

temp shifts could also be an issue. i know here in ohio its been going from 50-70 degreese F within just a few days, and it's made that shift twice and its about to happen again with alot of rainfa.

[Ravnis]

How are you adding the hydrated lime? Adding hydrated lime directly to the fish tank can clog fish gills and result in fish kills.

[GreenFin]

Any update, Harry?

Others here have already covered my initial ideas (lime causing problems, low temps, low O2) and suggestions (dissect a couple).