Backyard Aquaponics
A place to discuss aquaponics

Hi all

Woke up this morning to find all my 40 trout dead, some floating, but most head down on the bottom.

System has been going very well for last 3 months with no issues. Tank was looking a bit dirty yesterday so cleaned using a pool pump and sand filter. Sprayed the bottom off and the sand filter simply cleaned the water and returned it to the pond. Have done this before with no I'll effect.

My 40 silver perch and 3 gold fish all fine. trout ate well yesterday afternoon and show no signs of anything. No slime even. Have removed all the dead fish and the other fish are acting normally.

Test results:
Temp 13.5
pH 6.6
Ammo 0.25
Nitrites 0
Nitrate 100

2000 liters
4 x 500 liters grow beds
Flood and drain system
Nothing added for 3 months


Any thought or reason any one can think of?




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Absolute bummer Bryan

Could there have been any chlorine from the pump gone into the system - trout are certainly prima donnas compared to SPs

Condolences brybank
Could be copper residues in the sand filter from anti algae products, but as you have used it before that possibility seems unlikely

That is terrible news Bryan. I can't visualise the sand filter set up, are you able to post a pic?

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Just picture any normal pool filter Faye - they're pretty much all sand filters these days.

But does it get disconnected when not in use, and is there water left in there that goes stagnant, or does it dry out.
I know how my pool one works and it contains zeolite, but it filters my pool not a fish tank.

Hi Brian, just checked on your system thread and one of my concerns in your system has been the use of zeolite.
Do you have any back up aeration for your system?
Although you have 2 BYAP beds that hold 1000 litres of Hydroton, I very much doubt that the other two beds have the same volume of filtration. It may just be a coincidence that you had vacuumed with a pool pump. Time to consider what the effect may have been in upseeting the environment of the trout?
Do you still have the waterlily in there, or is there anything else in the fish tank?
For all the trout to die in one hit I would suspect contamination or aeration issues as trout compared to silver perch are fussy in that respect.
I do hope that we can find some reason for you. Please keep us updated so that we can help others - me condolonces

Sounds like aeration problems to me. Trout need lots of it

My guess would be oxygen, as the trout get larger their demands for filtration and aeration increase. Hence why I am harvesting mine from 250gm to reduce the load on my system since at 400gm each my filtration would not cope.

The sand filter I use is for the pond only and I only use it once a month or so, I backwash and flush it before I use it. The aeration would have improved a lot because the water return is above the water level. What could have been a problem is because of the back washing and rinsing I had to replace about 20% of the water volume with tap water. I normally top up with tap water so did not think it would make that much difference, but could have been too a large volume.

How much "stuff" are you cleaning off the bottom of the FT each month? Build up of any gunk is a sign of surplus feeding and/or insufficient pumping. If too much gunk accumulates in one place it can become anaerobic and when you disturb it, it can release clouds of toxins into the volume of water. Sensitive fish like trout might succumb to this when other tougher species don't?

I'd be revisiting your system design to improve FT floor suction and reducing the amount of waste produced, regardless of whether the sand filter was partially to blame for the unfortunate deaths.

Even if your built up food is not going anaerobic, I have found that disturbing a pile of food (mixing it up with a stick) can spike your ammonia. I'm not saying that this is the case here, just adding to bunson's comment.

It makes some (maybe) sense to me that if food is depositing in a low flow area that there also might be insufficient flow to mix the majority of ammonia produced by this rotting food around the tank. Resulting in a localized high ammonia area.

Certainly the fact that all and only trout died, and no other species, points to something else. Unless trout are more susceptible to high ammonia???

Hi Faye

Still have the water lilly and this may have something to do with it as I clean the top of the pot with a jet, there did not seem to be a lot debris that came off.
I checked my levels again and they are the same.
You are correct in that the other two beds are half the volume of the ones I got off you guys.
There was only two 25 liters of zeolite added to the system and if they were the cause of the issue would the ammonia levels not reflect that?

The amount of debris on the floor that I disturbed was minimal, there was no food only algae and fish poo, not enough that I could not see the bottom of the tank at any stage.

Has any body lost trout from doing a 20% water change with tap water?

While I was filtering the water I also changed the system from a flood and drain to constant flood for about 4 hours.

I have the standard two output air pump with back up batteries that I got from you which has not missed a beat.

We also got a fair bit of rain on the night that they died.

Just giving you all the information I can, in case I have missed something.

Thanks for all the input and help.

Bryan

I have read so many times about fish deaths after rain, not saying this is the cause though but it often makes me wonder.

I lost 5 trout last year after a heavy rain, its possible the rain run off from my patio was picking up something from old rotting leaves etc in the gutters. I never really figured that one out.

I've noticed sometimes my trout seem to go off their feed for the rest of the day after even a 5% top up of the water level, no deaths that I could pin down though...

20% tap water could have done it if the chlorine levels in the town water were high for some reason.