Aquaponic Gardening

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I seem to have gotten to that time when my fish, those around 3 inches long, start to die for reasons I can't determine. Two this week. The pH is OK though a bit low (and I'm adding lime to raise it), the ammonia is zero and the nitrite is zero. I am transitioning the larger fish, around 6 inches, to the adult food though they don't seem real interested in it. My plan is to exchange out about 1/3 of the water today to see if that helps. Any other suggestions? 

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how big is your ft?  how many fish, hand how much gb? what are you doing a water change for?  a big ph adjustment will stress your fish, try to keep it under .2 change/day

and adding 30% chlorinated water will stress everything (fish and bacteria)

do you have any additional aeration running?

Actually I have fewer fish than recommended. About ten or so larger ones and then two recent births of minnows. the water I use in the tank is from a cistern in which I collect rain water so chlorine isn't an issue and the pH of the cistern water and the 300 gallon fish tank are very close. I'm running an aerator with two stones so I'm pretty sure that DO isn't a problem either. That's what makes it so troublesome. The dead fish this a.m. didn't have anything on its surface that looked problematic though it's eyes were white. I checked last night and didn't see it so was surprised to see it floating this a.m. 

Is there any possibility that adding iron could be the culprit? I added a teaspoon of chelated iron on Sunday, as per Murray Hallam. I put it in the siphon. It seems unlikely but...

No adding Fe-chelate probably isn't it...How are you collecting the rain water? Meaning what are all those components made from?

I'm pretty sure that's not the problem. It's all PVC and food grade tanks (from which we use the water) except for a stainless UV filter. I did spray the beans with pepper spray but covered the grow bed to prevent it getting on the rocks. The fish tank is in another area so overspray couldn't happen. It's conceivable that some got into the sump tank but, again, I tried to be pretty careful. I live in the FL Keys so temperature is not a factor. It seems to happen when the fish get to be about 3 months old. This is the second time I have had dying fish. Last time they all died and I had to start over. I'm hoping that won't happen again. I checked my notes and I had changed out the water last time and that didn't stop the fish die off so I have changed my mind and won't change out the water. 

How low was your pH? And why was it low? As Vlad said, check all of your rainwater components for possible source of metal toxicity...galvanized gutter or flashings, zinc anti-moss strips, copper...What kind of fish?

I'm not sure why the pH was low. It was about 6.4. We had a heavy rain last night and I think that's what brought it down because the rain gets into the sump tank. The fish are tilapia. Would galvanized gutters affect the fish after 3 months when it hadn't affected them before? I'm pretty the gutters are that plastic stuff they use now. I'll check but I would think, and I could certainly be wrong because I have so little experience with fish, that it would affect the fish right away. 

Metal toxicity is an accumulated thing, adding slowly to the demise of fish until it reaches a lethal limit. Galvanized gutters will always leach zinc, yes, as will roof flashings. Even iron has a toxicity to fish, so it is even possible that your most recent iron supplement was culprit if iron was already high? Vlad will know more there, he's iron-man :) It's also certainly possible that you have a fish disease of some sort. I've lost some tilapia, about 4 out of 25 Hawaiian Golds, from disease I suspect. And they were all runts, the most recent was about 3" when the rest of the litter was 6". They were pale and hollow like they were starving, yet were the first to hit food when fed. My guess is some intestinal parasite. However, it was always only one or two, and all the others were and are still fine. Matthew Ferrel knows his fish, I'll see if he can chime in. I neglected to take any pics, do you have any pics comparing the dead to the healthy ?

6.4 is ideal for plants, and acceptable for tilapia, so I wouldn't raise it. Rainwater is unlikely to bring pH below 7, unless you live in Detroit, so it is likely that you have soft water and nitrification is holding it low. Good for you. Don't touch it. How many fish have you lost, over how much time, out of how many total? Also, what's the temp? And did the rainfall substantially lower your temps?

Hmm. Well what you say is certainly possible. I had the water tested by a reputable lab and no trace elements showed up but they are, of course, testing for human use. I had two fish die in the last week. One was pretty small, probably only 3 inches and today's fatality was about 4 inches. If I can't use cistern water I will have a problem. How long should city water with chloramene in it sit before it's safe to use. Maybe I should add some of that to see the effect. I can run it into a separate tank, let it sit and then pump it into my fish tank to augment what I have in there. 

I'm not a chloramine expert, I have well water. I believe there are inexpensive filters that attach to a garden hose. The filter may even pull out zinc, IDK The other point with water testing is that the cistern may not accumulate toxic levels. Water and minerals go in, water and minerals go out. But in the FT, water and minerals go in, but only water goes out thru transpiration and evaporation. So if plants and fish do not use as much mineral as is going in, then you'll get accumulation. Some minerals harmlessly precipitate, others (zinc) will remain in solution to a toxic level.

I do have two filters on my cistern. One is a carbon filter and the other is for particulates. The testing lab turned up .13 milliliters of zinc in a liter of water. Is that enough to kill fish?

start at page 9 for zinc toxicity (and as it relates to ph)

what kind of fish do you have? (besides the minnows)

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