Backyard Aquaponics
A place to discuss aquaponics

Hi everyone, long time peruser, first time poster. I would just like to say thanks for all I have learned so far. It has been smooth sailing... UNITL TODAY!!! :l

The System:

25 Blue Tilapia
130 gallons of water
Ph 6.8
Water heated to 70-80 throughout the day
Very Low Nitrites/Nitrates/Amonia
Well water very hard but has been improving
System running for 4 months now without a single fatality
Big, healthy plants in the system (tomato, jalapeno, red onion, spinach, brussel sprout, basil, strawberry, lettuce, kale, carrots, broccoli, peas at the moment.

I monitor the fish daily and have not seen any itching or any other odd behavior. The fish have been healthy and active and remain so, except the dead ones. :l I have the fish separated into 2 tanks, all connected to the system. This morning I noticed 3 dead fish in my smaller tank, one looking to have been dead for a day longer than the others. Just a couple minutes ago, I noticed a fourth dead fish in my larger tank where I keep all the big guys--hence my post. The strange thing is the fish I have lost so far are of the biggest I have presently. There are 3 or 4 very small fish still and they seem to be fine. I examined the dead bodies and they appear to be in full form, no missing scales, nothing wrong with their eyes, mouth, fins or vent. I am stumped and sad to have lost some friends. I humbly await your suggestions!

More system history: A friend of mine catches crawdads here locally near Sacramento, CA. I put a few in my bio filter to eat up some of the trash. Unfortunately, before I realized the species was intensely territorial, a battle had ensued leaving only one winner that still walks the waters til this day.

I was having a lot of algae growth also in some of my peripheral tanks, so I have been grazing 7 2in goldfish from the pet store. The goldfish all seem to be in positive health and spirit and none have been lost in this most recent tragedy.

At first, my Ph was quite high being on well water and all, so I treated the water down months ago with the help of a little HLC and peat moss. The water has been stable for near 4 months now.

What are you using for aeration. Its possible with high temps and algae the system may be starved of DO. This usuall sees the bigger ones go first. Were their mouths open when you found them?

That was my first thought as well, especially with the biggest ones going first.

I made 2 venturi aerators, one for each tank that run at all times producing many small bubbles. None of the fish have been at the top of the water gasping for air since I started the system 4 months ago. I can add another venturi, or alter the flow to allow for more oxygen, but haven't since the fish have not been gasping.

I would also like to mention that the all the fish have good slime on them.


Thanks for the quick trouble shooting so far. It's exciting finally being on the receiving end of these posts!

We might need some pics to help assist.

Here's pictures of a close up of the fellas, smaller nursery tank and the fallen. The water is deeper than it looks and crystal clear with a slight golden tinge to it.

Warning: Fish death ahead

Is there/could there be some debris/waste anaerobically decaying in amongst the rocks? If this is disturbed, there could have been a release of toxins from the locale?

We aren't allowed tilapia here, so my knowledge of their requirements is very limited, but in general unless fish are nesting, I'd not have anything which could harbour nasties, or regularly flush the rocks to ensure nothing is creating dead spots.

Very astute observation! I will remove and clean the rocks tomorrow. Thank you.

On a side note, for this to be true, the toxins would have distributed along the whole of the system water. That could account for the death I had in the bigger tank, in which no media lines the bottom. How does this sound?

Its a possibilty. Id remove the rocks all together, they serve no positive purpose.

The fish on the far right of the last pic looks like its been decomposing for some time, was it left in the FT like that for a while

I pulled the first 3 fish out early this morning and one had been in the tank no more than a day. But I'm thinking if the first fish had been dead longer could this account for the other 3 deaths? And how would only bigger fish being affected be explained? In that case the water would be contaminated and I'd need to add fresh water. This seems to be a good candidate as the cause of my problem. Thank you.

Yea, Id put my money on that to be a likely scenario.

First fish dies, reason unknown, very hard to say why. Then usually a few follow due to stress, contamination etc.

Might be best to salt to 1ppt (pool salt), back off feed and increase DO. Keep an eye on the others for fungal issues etc.

Forgot to mention the obvious --> remove the fish to a "clean" environment BEFORE further disturbing the rocks, then do the cleaning/extraction and finally a water change, salt (1-3ppt), check temp and pH before returning the fish. Aerate well, and pump continuously for a few days and observe closely.

Thanks for the clarification everyone. The hospital tank is all set for tomorrow's intervention. Put some fresh water into the system and haven't lost anymore fish in the mean time. Trying to figure out how to get salt to 2 or 3 ppt in 50 gallons of water now--next on the list.

That would be ~0.417 pounds of salt per ppt (so times by 2 for 2 ppt, 3 for 3 ppt, etc.)

Hey, thanks for the calculations! I am also a low carb (low gluten) TNPer haha.

So I've heard different things about the type of salt to use. I have a lot of table salt. I've heard pool salt mentioned, along with plain sea salt. Half a pound seems like a lot that surprised me.


I will be transferring the fish into the hospital tank and it will have much more salinity than my system tanks. I was wondering do I put the fish in a bucket of system water, floating in the hospital tank to normalize temperatures and then slowly add the saline water to the bucket over a period of time, and then finally let the fish into the hospital tank?

Thanks again everyone.