Backyard Aquaponics
A place to discuss aquaponics

I have a 3 year old flood and drain system that successfully grew out tilapia. It has a 300 gal. Tank and 9 media filled grow beds. The plants have produced many tomatoes and peppers. Last year I harvested the tilapia and added 50 perch. After they were a year old they started dying off. I harvested some but by the end of May they were all dead. I have not been able to attribute it to any water quality issues..The perch supplier said to wait 2 weeks before adding more fish and I waited longer than that adding pure ammonia to keep plants alive. I then added goldfish 20 of them in a 300 gallon tank. All of them were dead in 2 days. Then I added koi and they died in 2 days. The temp is 64, ammonia .25 ppm, pH 6.6 to 6.8, nitrites 0 and nitrates between 80 and 160 using the API kit. Are there fish viruses that could still be in my system? The fish have no tell tale signs of cause. I really don't want to drain the system but maybe I need to?? Would love suggestions.

Are they gasping for oxygen? IE at the surface?

I have no clue at what the issue may be as your numbers look good exept ammonia although very low. Ever add salt? Salt level?


If you have to sterilize the system, I would not drain it but pour chlorine into it. Let the pump run with the chlorine. Test for chlorine a few days later. When it's zero, re cycle the system with ammonia. Just my opinion on sterilizing system. Your money may vary.

I did add salt a while back but have no way to test the system for residual salt.

Sorry to hear about your fish

It usually takes longer than 2 days for a virus, bacteria or parasite to kill that many fish so it's more likely to be something environmental like pH, temperature fluctuations, dissolve oxygen, ammonia, nitrites, or some contaminant like a metal or pesticide. In the case of the goldfish if the water they came from was too different or they suffered during transport from poor water quality, it's likely they died from shock at too rapid a change or poor initial water quality during transport than from something in your tank water.

1. If you have a local aquarium shop or friend with a test kit and they are will to cross check your results sometimes the kits go bad.

2. Someone mentioned this before I got it typed but try salting (no anti-caking agents and you want un-iodized) the water to 1 ppt for stress and to help the fish develop a slime coat. Check with the aquarium store, some will test the salinity for you with a refractometer if you take them a sample.

3. Give a critical look at your system and see if there are any sources of contamination like roof runoff. You may want to post pics because we might spot something you don't.

4. If you have lots of algae in the tank block the light to get rid of it. It's normal to have some along with bio-slime along the sides of the tank (and you don't need to mess with it) but if you water is looking green you should do this. Algae cuts down on the oxygen at night and also causes the pH to fluctuate more over the course of the day.

Hope this helps

Edit: Check your ammonia bottle just in case it contains a detergent.

Scotty,

You mentioned roof runoff....

My top up water comes from a 750 GAL water collection system from my shingled roof on my house. Is this a bad thing. Never crossed my mind. Been running it like this for 4 years.

Thanks for the ideas. The system is indoors so no chance of roof runoff. I will buy a new test kit and try that. I don't have any fish right now but should I add the salt anyway? I did add salt when the perch were still alive which would have been May. I won't be able to get fish for a couple of weeks since I am leaving on a trip. Will have my house sitter add ammonia to keep plants alive.

Also, water is clear but tank sides have a lot of algae. I could spray that off.

I can't say for certain but I wouldn't recommend it to someone just starting their system (especially since asphalt shingles are a petroleum based product). Asphalt shingles usually shed a lot of grit when they are new (and probably some other things). There have been a few systems that it looks like runoff from a shingled roof was the cause of fish kills but confirmation is tricky. Usually the systems worked fine for a year or two and then started having problems. It may not be but seems likely there was something toxic in the runoff that built up and finally hit concentrations that killed the fish (could have been their gutters or another source as well ). There are a lot of people doing AP using water from rainwater cisterns successfully but my impression is that usually they aren't using shingled roof material.

Wish I could tell you more but there just isn't enough information

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tmwharton

You probably still have enough salt and I'd leave the algae for now, have fun