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My tilapia are dying in my aquaponics tank and I don't know why. I've done everything I can think of: changed out the water, stopped feeding them, checked pH and ammonia (both OK), treated them with fish treatment liquid. And today two more are dead with only 7 or 8 left. Does anyone know someone who does fish necropsies? I need to see why they are dying. Could be a virus or something else. I live in the Florida Keys so it's not too cold and not too hot yet. The fish are about 6 inches long. 

Terrible!! Any other suggestions? 

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Another tilapia died and I noticed that the gills were red. Yes, I am aerating the tank so I don't know what this means. 

What are your PH, ammonia and nitrite levels?

pH and ammonia good. pH about 6.5 and zero ammonia. Haven't checked the nitrite but will. 

O2 is probably OK or they would all be dead.  

If it's not nitrite, then you might want to read up on tilapia virus that is affecting some commercial systems.  I'll see what I can find.

Have you introduced fish recently?

No. No new fish. I wondered about a virus. One that died yesterday had red gills. 

Checked the nitrite today. Zero. It must be a virus or the water. No more dead ones for 24 hours! But only about 8 or 10 left. 

If it is a virus then possibly the survivors are immune.  Thai is a scary thought that it might be your water.

Yes. Scary. We get all our water via the Florida Keys Aqueduct Authority and they routinely mix in a small percentage of what they call "brackish" water, which is higher in salt content. In addition, it comes in at pH 9.4! I have a 5000 gallon cistern that I can't use for the fish tank because of the presence of zinc (which killed all my fish five years ago when I first started). I'm going to install an RO filter on the cistern water, which removes zinc and other metals, and switch back to the cistern water, which is rain water with no chemicals. 

I suppose the zinc is coming from your cistern tank.

Salt water shouldn't be a problem for tilapia.

Are you using an API test kit?

API? Yes. The Zinc is probably coming from the metal downspouts that bring the rainwater to my cistern. 

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