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Hey team!

I usually like to figure stuff out myself but I guess this forum is here to help!

The last few days a few of my blue tilapia fingerlings have been dying is the break down

800 L tank...the same of grow bed
All water quality tests normal, ammonia 0, nitrite 0, nitrate 5-10, ph 6.5
58 fish 2-3 inches feeding 42% protein trout food, all been eating except the 3 that died who turned pale grey and sank over last few days. Gills and major organs seem fine and no sign of lesions or disease. Plenty of aeration from bell syphons and recently added air stone...although a few times I have seen them gulping at surface after a bigger feed but pretty confident it's not a DO problem

These guys were troopers during cycling and only now when everything is doing so well I start losing fish??

Any ideas would be appreciated! Do I just put this down to weaker fish dying off? I have an aluminum screen over drain would this be an issue? Grasping at straws peeps!

Thanks in advance!

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Mine looking pretty normal in water column Jim...the ones that are ill tend to sit in bottom

I'm a little late to this discussion, but I too had a similar experience with 50 blue tilapia in a 300 gal tank.  Everything was going fine for at least the first month and the tilapia were feeding and growing well.  Then suddenly began losing 2-3 fish a day for a week until I took action to filter my water and do a near 50% water exchange.


Tilapia are very hardy fish and can survive in crowded conditions.  Also they can withstand high amonia levels, low pH levels, and even a low DO level.  I would not suspect anything related to temperature, pH, or DO.  I would be concerned with anything toxic that may have entered the water.  Any additives, insecticides, or even rain water that may be contaminated, I would suspect.


In my case, I was a little over zealous perhaps, trying to maintain my new plants with Maxicrop seaweed, cheleated iron, and even neem oil to control aphids.   I also used rain water that had run off the roof through a new aluminet shade cloth.  All water testing was within normal limits.


Now the surviving 20+ fish are doing fine and growing.  In the end, I suspect it was the neem oil that ran off my pepper plants into the grow bed and then became toxic in the water.


If you suspect something in the water is killing off your fish, use a swirl filter and discard any solids, then do a water exchange up to 50%.  I used chlorinated tap water without any proplems, but I did the exchange over 2-3 days.


Hope this helps, Nick <>/p>

Yep, looks like nature fixed your over crowded tank... 

300g/50f= 6 gallons per fish

300g/20f= 15 gallons per fish

Just what I have found works best...

when the fish get too big; the system crashes in short order

Well looks like my die off has stopped for now.  A total of 13 fish died.  Have not had a fish die in a week, longest it has been since the die off started.  Started with 50 fish in a 275 gallon tank and 175 gallon sump tank now down to 37.  Things I did in order:

0) Took tank readings (all normal, Ammonia was 0.25 ppm rest were 0, Ph was 6.4)

1) Added air stone in sump

2) up the Ph to 6.7

3) Cleaned the pumps filter, really dirty and was slowing the water pumped to the beds and fish

That is really it.  Pretty much a mystery to me unless Ph was the culprit...

overstocking was the culprit

it was a combination of fish load and #3 dirty filters; i.e: living in too much solid waste.  Let that solid waste go into the grow/worm bed if you aren't going to be able to service the filter regularly, that's what most growers do.

Hi Jim,

I am sending it to the grow bed but also the fish tank as I am running CHOP2.  Should I just take the filter off and let the solids go through the pump.  The order I have from the pump is grow bed 1, grow bed 2 and then the fish tank.

Jim Troyer said:

it was a combination of fish load and #3 dirty filters; i.e: living in too much solid waste.  Let that solid waste go into the grow/worm bed if you aren't going to be able to service the filter regularly, that's what most growers do.

Hi Keith,

Even though the fish were only 2 inches?

Keith Rowan said:

overstocking was the culprit

smaller fish eat more food (so poop more) and are much more active than adult fish.. at least the tilapia i've raised..

fry can eat anywhere from 5 to 15% of their body weight daily..

adult fish eat around 2% of their body weight daily.. so yes.. even though the fish were small.... it's a problem

Just lost a 20 oz Blue Tilapia...WTF?

I have had my system cycled for nine months:

This morning I found a big boy just barely swimming near the top of the tank...I felt the best thing to do was fish him out and dispatch with him as humanely as possible...clunk on the head and an Ice Bath.

My water temp is 82 degrees, I'm in Miami...there are fifty more in the tank who appear to be fine...some are four inches and then up to 22 oz.

ph 6.6

ammonia .025PPM

nitrite 0

nitrate .25ppm

lots of DO from pump return splashes and air stones..


Thanks for your response, in advance

Condolences Ned...

That's a big fish!  How many gallons of water in your system and fish tank?  Has your plant load changed?

Get started on a 50% water change to reduce any poisons that may be in the system.  Reduce the feeding schedule and amounts by 50%.

Be sure to check the depths for other dead, or unhealthy fish.   Be vigilant!

Good Luck! Keep us updated!


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