Backyard Aquaponics
A place to discuss aquaponics

Hi All,
I have a 1500 litre system and 4 days ago dropped 35 silver perch 4cm into the system. Since then i have had 1 or 2 fish dying each day. They are not gasping for air at the top of the tank but don't have a method for testing DO currently.

ph - 7
NH4 - <0.05 mg/l ppm
No2 - 0.7 mg/l ppm (High but i wouldn't of thought outrages)
No3 - 10-15 mg/l ppm
Temp - 11 degrees C


I do have a large Venturi running into the tank which is noisy could this be stressing the fish?

Also they don't seem to be active at feed times have been using a sinking native feed 2mm that i have been crumbling up.

another thing is lately have been having heaps of rain in Vic and the system is outdoors and has added a lot of water volume not sure if this could be effecting things.

Any suggestions welcomed

Any Ammonia and/or Nitrite is undesirable when there are fish in the system, especially Nitrite. In a well balanced, properly cycled system, the Amm and Nitrite should always be 0.0ppm.

The higher the water temp and/or the pH, the less Amm it takes to be harmful to your fish. At the water temp and pH of your system the Amm would not be the issue. The Nitrite may be the issue, especially if it had been higher in the past. Add plain sea salt at 1gm/Ltr to reduce the effect of the Nitrite. If it gets above 2.0ppm you may need to consider partial water changes to reduce it. Don't forget to add the salt to the top-up water.

Another couple of things to consider. Was there a big difference in pH between the water the fish came from and your water?... A temp of 11C is low for Silver Perch, but especially so for small 4cm fingerlings.

Thanks for the response, i have added 1 kg of sea salt to the system today and re measured

pH - 6.6
NH4 - <0.05 mg/l ppm (The lowest reading my kit goes down to)
NO2 - 0.05 mg/l ppm
NO3 - 15 mg/l ppm

Temp still down at around 12 degrees

You may have had a nitrite spike that you didn't catch with testing. It's pretty common to continue losing a few fish at a time over a long period with this sort of problem because they've already suffered the damage. Salting is good also increasing the aeration might help as well. Go easy on the feeding - your numbers aren't bad at the moment (nitrite was too high earlier though) but your filtration probably isn't well established at this point. Stop feeding entirely if the levels climb or they aren't eating anyway (Fish go off their feed while adjusting or if something is wrong. Watch for any fish that die and sink to the bottom - remove them or they will start to cause ammonia and nitrite problems). It's better to feed less at each feeding so the spikes, if they occur, won't be as bad. Eventually the filtration will become more established and will be able to handle more.

Unfortunately over night i have had mass deaths in the tank 10 fish dead. Water results haven't changed since the other day fairly the same.

took water sample this morning and

Ph - 6.6
NO2 - 0.05 mg/l ppm
NO3 - 5 mg/l ppm
NH4 <0.05 mg/l ppm

Water temp has risen a few degrees to around 14


I did top some water off yesterday and used water conditioner,

i also recently installed an RO water filter on an auto top up on the sump tank not sure if this maybe is contributing.

All my beds are fully planted out no more room and the NFT is actively producing really large lettuce heads, plants are looking really healthy. But not the same can be said for the fishy's.. : (

Sorry to hear about the fish. Typically large die offs like this are due to physical changes and not disease or parasites. Here are some possibilities -

1. Previous exposure to high nitrites or ammonia.
2. Low oxygen levels due to lack of aeration or high algae levels (algae use oxygen at night)
3. pH or temperature shock during transfer.
4. Zinc buildup or some other toxin due to runoff from rainfall. For zinc this usually takes awhile before it occurs so I wouldn't expect it to be zinc but it is possible.
5. Stress by itself is sometimes enough to kill fish. The salt should help with this and the nitrite poisoning issues but if the damage was done, who knows .
6. Look for any wounds that could be caused by an animal or by components of the system. Also look for anything else that might be off about the fish that died.

I really think this has something to do with the initial transport or transfer into the tank. You may not be able to save the fish if the damage is already done but keep looking and see if you can figure it out.

Thanks for the responses
I have lost another 5 overnight and noticed there is significant gill damage on a few of the fish (missing completely in one instance). The remaining fish are now trying to swim but are spiralling and swimming upside down so there time is limited.

https://photos.app.goo.gl/o9PLPkPTbnwwkqNV6

Just some more photos & Videos of my setup might be something i am missing

https://photos.app.goo.gl/chQs1E8c6Cc2k4S39

Was the system cycled before you put the fish in? & how old is it?


It may not be the water quality,it might be a problem from where you bought the fish.
I saw your video & I googled it to see what might be the problem,most things said swim bladder problems and a bacterial infection.

On may 5th you said the PH was 7 & may 6th PH 6.6,but looking at the strawberry plant,it's showing slight Iron deficiency.Are you sure you're reading the tests right?.Shaking bottles properly etc?.It's possible the PH is higher or fluctuating a lot.

Like scotty said about the Zinc,are there any other metals in the system? Aluminium or Copper?.And did you wash the clay before filling the grow beds?

Thanks for the reply.

The beds have been installed and cycled for about 2 months (With goldfish in the sump tank before adding silver perch), the clay was washed in batches before going into the beds.

The drop in Ph was from me adding a little acid in, was aiming for a .2 drop and overshot.

I had an iron deficiency due to not supplementing any iron into the system in the beginning and probably planting too heavy for the amount of fish i had at the time.

Maybe the Pump Impeller on the submersible other than that everything is PVC. Another thought i had was what about the treated pine box and rain water, could the water running in off the lid capture toxins?

I notice that you are using rain water .What sort of roof are you catching it off ? If you have a galvanized or zincalume roof that may be your problem. If that is the case you can paint the roof so that the rain doesn't touch the metal. Usually they don't all die at once when this is the problem but just one or two here and there. Even a plastic roof and a zincalume gutter can cause the problem. In America you call this metal galvalume .

I'm sorry,I was going to say that but forgot.Sorry but it was 6 am when I wrote it.

Yes,treated wood will do damage (hurt the fish).If the rain came through the wood & into the water.But what about the gold fish?Did they last 2 months with the system in the current state? or did you add the wood later? & are they still alive?

There's also Magnesium & Nitrogen deficiencies,if the fish aren't eating (or living) it's obvious why.

Btw,the system looks good!