How I DECIMATED my aquaponics system and I have no idea why!

[Jeff]

I don't know if this is a cry for help, or just my last ditch effort to figure out what the hell is going on.

BACKGROUND: I've had my established backyard system going fine for TWO YEARS now. In those two years, I don't think I've ever lost a fish. So aquaponics isn't exactly new to me. My system consists of a 110 gallon tank and three 40-gallon grow beds filled with hydroton.

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All of the sudden, roughly two weeks ago, fish began to die. Since the last 14 days, I've gone from 29 fish to about 8! Yes, you read that correctly.

The way it started was that I found about 6 dead ornamental fish (on the smaller side) all dead in the corner of the tank. Some were partially eaten so they may have been there a few days. Since I had so many fish though and never an issue, I hadn't been checking the water as much as I should.

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So my first thought was, "Oh crap, was there some kind of ammonia/nitrite/nitrate spike? What could have killed them?" I checked all those levels with my test tube kit, and the only thing that appeared high was the ammonia (possibly 0.5ppm). Perhaps the ammonia was high because of the dead fish sitting in there, but more than likely, I think it began to slowly rise because all the fish were growing larger, and contributing more waste to the system. I think having 29 fish in a system with only 110-120 gallons of water is too much (but didn't seem like it when they were all babies).

But I digress.....

What could have killed them? I know.....perhaps it's because I had hadn't vacuumed out any fish sediment that may have been collecting around the pump inside the tank. You see, my pump cycles water from the tank to the grow beds, but inevitably, any solids that don't get sucked up sit around the sides and back of the pump. Well, there was a mountain of sediment in there.....so I used a wet-vac and sucked it up.

Thinking that would have some positive impact, I was surprised when more fish started dying.....this time, some healthy LARGE goldfish.

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So I immediately went to the pet store with a sample of water, and had them test it. They said it looked fine, but the nitrates looked high. (NOTE: My nitrate readings at home looked fine, but the pet store used those little 5-on-1 test strips which indicated a high nitrate level. Strange, I thought.....possibly an error? I always heard those strips weren't that accurate.) Either way, they recommended a water change.

Now here is where I made my first big mistake. I did an aggressive water change (over 60% of the tank). My tank is about 100 gallons, by the way.

Up until this point, I've always just topped off water when it evaporated....never did a water change. Topping off always consisted of putting my hose into the tank and filling it until it was full (estimated about 10-30 gallons at any one top-off). Never did I ever put in any Stress Coat formula or Salt.


So after this drastic water change, within a few hours, I saw more "healthy" fish die. I believe that happened from shock: too much water changing places, and possibly a temperature difference from the hose?

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A few days later, after it seemed under control, I started to see my Koi dying. All water tests appeared to be fine (pH, ammonia, nitrate, nitrite). The water temp was in the 70's or low 80's, and that's never been a problem. Always had good water flow and oxygen being returned from the siphons.

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So like an idiot who means well, I decided on ANOTHER WATER CHANGE. This time, I took a bunch of 1 gallon plastic water bottles, filled them with water, let them sit IN THE TANK to get the temp acclimated, and then poured them in. I also added the right amount of Stress Coat formula and 1 ppt of salt.

I even built a new 15 gallon radial flow filter, to help collect any extra sediment from the fish bed and serve better filtration.

Despite all this, my fish are still dying (at least once per day).

I checked my ammonia and it appears a little high (between 0.25 - 0.5). I haven't fed the fish for 2 days now, and I have no idea why it's high. The only thing I can think of is perhaps the water changes from last week affected the nitrification cycle? What do you think?

Either way, I am totally helpless right now and have no idea what to do to stop the fish from dying. Any ideas?