Backyard Aquaponics
A place to discuss aquaponics

I have an IBC tote aquaponics setup in a garden shed lean-to, which I have been hoping to "refill" with tilapia I breed indoors in a smaller system built around a 55 gallon aquarium. But I can't raise the indoor ones to breeding age!


This is, if memory serves, the third time this has happened:

I buy twenty/thirty tilapia fingerlings [at approximately the price of frozen tilapia fillets at the grocery store each!] and put them in the aquarium. I don't have a huge growbed above the aquarium, so I have to be careful how much I feed them, but they gradually grow and grow. No loss for many months, and once they're big enough to not be food for the stalwart old goldfish in the outdoor tank put most of them there.

Now instead of continuing to grow and beginning to breed, the remaining fish end up slowly dying off. One week I'll find one floating, a couple weeks later two, the next month another one…!

This latest round:

2017 April 4 — put in ~25 tilapia fingerlings

2017 November 11 — fish now about 2–3 inches long, FIRST DEATH [pH 7.6, Ammonia 0, Nitrites 0, Nitrates just above 0]
2017 December 8 — second fish dead, did partial water change despite good numbers
2017 December 15 — third and fourth fish dead, moved 10 to outdoor tank leaving 10 inside
[found no fish dead after returning from the holidays]
2018 January 20 — two more dead fish this morning!

I just retested my water: pH 7.6 via API test kit (cheap yellow electronic pH meter shows 8.2), no Ammonia/Nitrites/Nitrates, Ca2+ may be high or test defective, TDS at 217ppm. The remaining 8 fish seem fine, eating and lounging around as always. (The fish are now around 2–3.5 inches long.)


My theories so far:

Nitrates? — With an earlier batch when this happened, my nitrates were way past 200ppm and I wondered if that was it. Has not been an issue this time. I think I've rule this out.


Fish fighting? — I have yet to see the current batch going after each other, and I put in three clay pots in December in case they wanted their own space. I don't think this is it either.

Water quality? — My growbed is suppose to be flood and drain via a bell siphon, but it gets stuck both at the top and bottom of the cycle. About every day I jiggle it so it at least advances to the next part of the cycle.


Unless there's something else I should look for, my worry is that I may have some anaerobic activity going on. Is there a way to test for those byproducts, or symptoms I should look for in the fish? Why would this only affect the fish once they're older?

[whoops, I see there is a "Fish Problems" board separate from the "Fish" — could a moderator please move?]

Those deaths do not sound alarming. I'm guessing a 100% survival rate is unrealistic.

Why would I have a 100% survival rate in the aquarium for half a year, and then once the fish get split up a 100% survival rate in the outdoor tank, but only a 10–25% — or even 0% eventually! — survival rate eventually in the indoor aquarium?

(They just started dying off this time, if the trend continues like it did the last attempts, pretty much all the remaining fish in the "breeding" tank will end up as sinkers/floaters within a few months again…)

I bought 10 tilapia and they shipped me 12... I had them all survive. The only one that died was the first female who had babies I removed her and put her in a tank by herself to let her try and hatch the babies without pressure of them getting eaten... she lost that first batch so I moved a male in with her and the male tormented her to death being that she was the only female in there.

Tilapia are in the cichlid family. They are very aggressive. It is recommended to keep them at a ratio of at least 3 females per 1 male if not more than that otherwise the males will pursue the females until they die. The alternative is crowding them in a tank to make it so they do not have room to be aggressive. I had all 12 of mine in a 55 gallon and they seemed to be OK no problems until that one death when I moved them to a different tank for selective breeding. There is definitely a male who is in charge, he sometimes claims half of the 55 gallon tank and pushes the other 10 in to the other half of the tank. I am about to thin them out to leave only one male in with the females because I have seen where one of the males had some damage to its fins that the dominant male must be beating it up. When they are young they have to establish dominance so you will see them battling to prove who is boss. Those fish are about a year and a half old now. I raised about 125 babies from them and gave away about another 100 babies last year.

I did have a few losses out of the babies that I raised from my breeders when they reached adulthood... I attributed that to fighting for dominance too but I also had cleaned my DWC bed which had a lot of detritus build up in it just before the deaths started so I might have released some H2S in the system to cause deaths but it went on for a while that I would only have 1 fish dead at a time so I don't think it was H2S I think it was dominance fighting because the deaths stopped once I started harvesting fish and reducing the numbers.

I would attempt to identify the males / females to make sure you reduce the number of males in the tank if you intend to breed them. The males usually grow faster (larger) but you can also look up how to sex tilapia... Its not the easiest thing in the world but I have used some blue or green food coloring and a Q tip and think I was able to tell fairly well after looking at quite a few multiple times... it is harder when they are younger though so you need to look at a lot of them to compare before you start to figure out what you are looking at. If you are using the tank in the picture I can't tell what size it is but I'd probably only try 1 male and 3 females in there it doesn't look very big.

I always expect and usually get a 100% survival rate for fish with proper quarantine and acclimation to temp and pH. My brother had a similar problem to you, and in the end it turned out that he did not wash his growbeds adequately before putting them in service. Since they were new hydroponic beds he figured they were good, but many manufacturing processes use mold release agents and other chemicals that can be difficult to remove. He dumped the new beds and washed them completely and the problem went away.

So if you didn't scrub the GB's and tanks in the system thoroughly with soap (I add some bleach too) and thoroughly rinse them, then they might be leaching toxins into the system. Tilapia are some of the toughest fish I have raised, but goldfish are tougher in many ways.

Anything else that might be toxic in your system - zinc, copper, brass, lead? Flexible hoses may have toxic plasticizers that can leach over time.

Thanks all for your tips so far!

I just had another one die this morning, saw it coming since last night.

To be clear, I am sure this is NOT normal. In many years with my large outdoor tanks, I have had exactly ONE fish die inexplicably: a random goldfish I found floating once one morning a couple years ago. [Explained deaths include all the tilapia fry the goldfish ate, all the fish that froze when the greenhouse blew apart one winter, a few that succumbed to a long winter stretch the heaters couldn't keep up with, and the half dozen that I did manage to harvest and eat overall all these years….]



Anyway, I noticed the latest indoor casualty half-dead before I went to bed last night. The others were sleeping normally, but this one was vertical in the water (nose down, tail up) and for the most part at the whim of the bubbles/flows in the tank. It was dead at the top this morning.

Besides the dying part, no particular signs of bad health (fins and scales in good condition) unless you notice something I haven't. All the other fish seem normal, swimming at a reasonable clip, interested in food, not interested in my hands near the water…


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As to the system, the pump and hoses are from a garden/pond shop in town and so presumably not an issue. (Using the same brand pump and some of the same hose in outdoor system). Siphons is PVC pipe/fittings guarded by ABS tile, again same as outdoor. Media is [forget the name] but something halfway between lava rock and expanded clay, from a local grow shop. There's also a very shallow layer of aquarium rocks in the bottom of the tank — I know any media down there concerns some people but as this is supposed to be a breeding tank I wanted a bit of "nesting material" and the fish have kept it pretty clean.


I top it off approximately weekly with some water that I let air out in a 5 gallon bucket, and no longer do significant water changes. The last round of fish when this happened, even 80–90% exchanges didn't seem to help much at all and so now I figure why steal everything from the plants.

If I had to call out one potential suspect plastic, the grow bed is a cheap plastic cement mixing tub with a hardware store bulkhead that cost about as much as the tub. (Both from Home Depot iirc.)

The other possible issue is that my flood/drain cycle isn't at all reliable so every day or three I manually drain the water before letting it get stuck back up top again. So anaerobic activity might be possible, but that's not sounding terribly likely either over on my specific thread for that: viewtopic.php?f=29&t=29413

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What should I try next? I'm tempted to put *all* these adolescents into the outdoor tank, and order a new set of fingerlings to see how they do in the system as it is right now. But is there something I should try fixing before I risk that?

It sounds like a buildup of toxins to me. Did you scrub the mixing tub with warm soapy water and rinse thoroughly before filling it with media? If not there is likely a manufacturing residue on the tub that is leaching into your system and killing fish slowly.

Are you just using tap water? Are you on city water or a well? I wonder if it isn't an issue with your water having something in it that you can't test for... I know I've heard horror stories in my saltwater days from people who use city water... the city uses chemicals to keep the city lines clean and they are supposed to be safe for human consumption, but the reality is that depending on how close/far you are from the city lines you could have issues with too much or too little getting to you which is why they recommend for saltwater that you have to use RO/DI or distilled water.



If you do end up moving the rest of the fish outside then I would consider siphoning out a bunch of water and try replacing it with RO or distilled water the next time around and see if it makes a difference with the next batch of fish.... your outside system being larger might just have more buffering capacity that it hasn't become an issue... or like my house if I was using tap water inside would be soft water where outside is hard water so could be a salt issue or something else in the water. My indoor tanks I only use RO for them... my outside system gets tap out of the hose (doesn't run through the water softener).

Two more fish dying in the aquarium, one yesterday and one this morning. I moved them over to my top-off bucket and have been aerating that to see if they improve at all. I might evacuate the remaining few survivors to the outside tank today.


I've been using the media bed tub for at least 3 years. I forget how I cleaned it originally, but it has had one media change (from lava rock to the hydroponic ones) with a good rinse/scrub at that time too although no soap.

As far as water, it has been a combination through the years. We lived in one city for the first batches, and then to a community well which now has gotten switched over to a second city's supply. Both cities' water quality documents refer to chlorine, and not chloramine. Same water source for unproblematic outdoor tank vs. aquarium.


What baffles me is why the fish are fine for so long, and then all die. Some sort of toxicity buildup could explain that. Maybe instead of moving the last fish outside, I will take them out temporarily and try a COMPLETE water change and see if that gets me through another half a year without deaths.

did you ever figure this out?

I still haven't narrowed down the cause any further, but I've been changing the water a lot more frequently. Happy to report that the five fish that survived the last die-off are still alive! (The ten I put in the outdoor tank were lost in yet another "heater stopped working" incident during a February cold snap… sigh… )

I aim to trade at least a couple 5 gallon buckets every Saturday, though sometimes it ends up being only one bucket every two weeks. The fish are a lot less "friendly" now; i.e. way less lethargic and a lot quicker to go crashing around the tank if I visit at an unexpected time.

The vegetables OTOH are suffering but that's not the main point of this tank. There's a few plants that do fine regardless, but I've been supplementng a bit more aggressively especially with the liquid seaweed to try make up for the nutrient removal that's happening alongside cycling out whatever mystery toxin thing is messing with the fish.

I need to try convince them to start breeding, as it hasn't happened on its own. The water might be a bit cold (not more than 75ºF now) but I'm a bit nervous this issue could have interfered with success there.

How old and how big are the fish now? Temps can definitely be an issue but my fish we're in the 4-6 inch range for females and 6-8 inch range for males before they started breeding, and then you'll probably lose a few batches before they figure out what they are doing. And that's assuming you have males and females in there and the males are manly males not sissy boys or they won't show any interest in the girls.