Backyard Aquaponics
A place to discuss aquaponics

Apologies in advance. I didn't want to have to be one of the people who posts this but I can't seem to figure it out.

My system has a 1500l fish tank and 4 grow beds consisting of a total 700l of media. The system is a constant flow system and housed 28 silver perch, now 23. The system relies on cascading water for aeration and has been fine like this for over a month. The system is about 2 months old and cycled in about 2 weeks as I had run the system before and used items out of a cycled fish pond. Yesterday the readings were ammonia 0-.25, nitrite .25 and ph just below 7. The nitrite and ph went up very slightly as the fish were eating heavily although they are still quite low. The temperature hasn't exceeded 15 degrees and gets down to 8 degrees some nights.

the water level rised and the drain pipe fell in the water recently which caused there to be limited aeration. I thought this could have been the cause but I fixed the problem over a week ago and the fish keep Dieing. I did the usual, salted to 3ppt even though the fish look almost perfectly fine, one had very slightly red gills but no where near as bad as I have seen in any photos. There is also no source of zinc near the system. There is some algae in the tank but I mean the rubies amount just enough to give the sides of the tank a slightly tinge of green. I have also recently covered the tank with shade cloth to parent algae growth.

Sorry I cannot upload photos at the moment.
Anything I have missed please let me know.
Any input is appreciated. I had 10 trout on this system with a smaller tank and less one growbed and had absolutely no problems.

Thanks in advance

What size are the Perch?

You say the system cycled in two weeks, did you cycle with the fish, or add them after cycling?

If you cycled without fish:

- Did the Ammonia and Nitrite both drop to 0.0ppm before you added the fish?

- How long after cycling then adding the fish did you start getting these current Ammonia and Nitrite readings?... and what level have they peaked at since you've added the fish?

If you cycled with fish:

- What levels did the Amm and Nitrite peak at during cycling?

- What was the pH and water temp when your Ammonia was at it's peak during cycling with the fish?

What are your GB dimensions you used to arrive at the 700L, ie: L x W x Gravel depth?... and what is the max water level in the gravel?

What water source did you use for the water in the system and what was the pH of it when you started?... Have you been adding anything to drop the pH?, if so, what, when and how much?

Why did you salt to 3ppt?... Did you suspect disease?

When you say one fish had red gills, do you mean the actual gills, or the area immediately around the outside of the gills?

I cycled with 5 fish fish. The ammonia spiked at 2 ppm during cycling and not sure about the nitrite as I was away during the time of that spike, the highest I read was about 1.5, it then dropped to almost 0 and nitrate spiked to about 100ppm.
I used bore water for water, as it went in to thetank it was 7ph then spiked to 8 but I caught it with a bit of hcl and held it around 7.5. Although that was over a month ago. Since then the ph has been hovering around 7ph without adding anything to alter it.
I salted because of suspect disease and it's not going to cause any harm so why not. Yes the area surrounding the hills was very slightly red.

What size are the Silvers?

Did you salt prior to the Nitrite spiking, or after it had dropped?

When were the other 23 fish added?... Had the Ammonia and Nitrite dropped to 0.0ppm before they were added?

GB dimensions, total gravel depth, wet gravel depth?

Where were you adding the HCl acid, how often, and how much did it drop the pH each time you were adding it?

The silver are from fingerling to med size 200mm. The 23 were added a few weeks after the system had stabilised 0 ammonia and nitrate.
My growbeds are 1000x1000x400, 1000x1000x250 and 1000x2000x150 I understand 2 of these are not the reccomended depth for filtration BUT i have been watching the amm and nitrite extremely closely and have been conservative on the food plus most over the fish are small only about 4 larger ones. I also have a 3000x800x450 grow bed to go in in the next couple of weeks.

The system he been running without adding anything for the last month and amm and nitrite Have Barely left 0 at all.
Hcl was added to a 20l bucket of water, 2 capfuls and then added to the system which brang the ph down approx a couple of points per day. Is it possible a spike in ph could effect fish a whole month later and have no effects at the time?
The fish are dieing at a rate of 1 per day and only the big ones. They all look perfectly fine then all of a sudden one is dead in the morning.

The fish that have died, were they the ones that were in the system when it was cycling?

Nope, the original ones are fingerling size and are doing well. the biggest ones have died off and are part of the 23 added after cycling.

One possibility - It sounds like these haven't been in more than two or three weeks. They may have suffered from conditions during transport or acclimation and you're just seeing the results of that now.

Maybe it was the transport. They did have a pretty rough transport 2hr drive. They looked quite sad after transport, especially the big ones. Although they seemed to recover 100% by the next day.
The 23 fish were added 22nd of June and first death occurred on the 19th of July.
Maybe we are just seeing the effects of the transport now

While it's still possible, that seems a bit too long time between transport and death. Sometimes ammonia or nitrite will cause problems and you'll get gradual die offs like this but it's usually within a week or two of the event so I'd keep looking for another cause.

Hopefully the deaths will stop soon. With your temps being low like they are, I wouldn't expect the drop in aeration to be a problem but it depends on how low it got and for how long. Direct injury to the fish would be one possibility but it might also create conditions that favor disease causing bacteria and what you're seeing can be caused by an internal infection.