Backyard Aquaponics
A place to discuss aquaponics

I need some advice regarding huge fish deaths in my iAV (sand bed) aquaponics system. The system consists of a 6000 litre fish pond and grow area consisting of manufactured sand (M-Sand -70% 2mm, 20% 1mm rest greater than 0.3 mm). The fish pond had GIFT (Tilepia) of the size 1 inch and less (around 1500 numbers). The water is pumped by a 6000 litre per hour pump for 30 mins onto the sand bed and there was a rest of 1.5 hours before the pump started again. The pond is aerator by a 700 watt sun sun aerator, with the help of 4 air stones.

Unfortunately the source water had huge Nitrates (more than 160 ppm, this was discovered later)

On day 3 (3 days since the fish was added), the aerator stopped working and was sent for repair. The system only ran via the pump. We continuously monitored the DO, and found that the DO never dropped below 5 mg/l, the system ran without aerator for next 9 days (i.e On Day 12 since the fishes were added, the repaired aerator was added again). Though the amount of bubbles was lower than when it was initially introduced, the aerator worked fine and DO reading was above 5 mg/l

On Day 7 (since the fish was added), there was a Nitrite spike (2.0 ppm). We didn’t know how to respond. On Day 12, we added 3 kgs of non iodised salt to protect the fish. By then the fishes had started dying ( around 10 to 15 per day ), and the fishes die even today (day 26)

On Day 17 (since the fish was added), the pump frequency was increased to 30 mins of pumping and only 30 mins of rest, since we felt may be the frequency is too low.

On day 21, a brand new aerator was added that gave a lot of bubbles.

Today is Day 26(Since the fish was added), the Fish is eating very less, even now its just 15 grams per day for the tank, nitrate is around 50 ppm and Nitrite is 0. Still there was around 12 deaths.

Please let me know whats wrong here, Am I missing something? how do I stabilise the system. Here is a photo of a live fish in the pond

sambavadekar,

I don't think we got your foto. Please resend it along with more fotos to help us better understand your system. Also send more test results. I assume you are testing water every day. Did you start water changes as a quick way to replace toxic water with good water? It is important to know the pH to know what is toxic for the fish. Knowing pH, Ammonia, Nitrites, and Nitrates for starters could help in diagnosis. High Nitrates by themselves may not be much of a problem. Several forum members have mentioned Nitrates at the 400+ ppm level without obvious fish stress.

That dose of salt might be too low for that amount of water. So was that 3kg salt to 6k liters of water? Or is there significantly more water involved (in sumps, growbeds, etc.?)

If the water is toxic, you may not have any quick enough options to fix it besides changing it out. Can you implement water changes?
Sorry to hear about your loss. Hopefully it is stabilizing by now...

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Sam

There's not many people on this forum familiar with iAV (integrated aqua vegiculture) The advice I can give is only in relation to fish health and conditions.

what is your PH, nitrite, nitrate, ammonia readings? What is the water temperature?

Did you cycle your system to establish the bacteria colonies for nitrification prior to adding the fish? If not, then the only way the system is going to stabilize is time to mature. Once we know what your water chemistry looks like we can maybe advise on how to help you keep the fish alive.

I don't see any information about ammonia levels which can also be lethal. I don't thing the nitrates killed them. It's difficult to say exactly what happened but It's not unusual to see deaths like this caused by high nitrites, where the deaths don't happen immediately. They are related to the original spike but are strung out over time and are due to internal damage and/or reduced immunity. I don't know how many you'll lose but I suspect you'll continue to have problems for a while because of the stress and damage already done. Tilapia can certainly survive this level of nitrite but the level of nitrite you recorded might not have been the peak level that the nitrites reached and the duration doesn't sound good either . Anyway it's not a sure thing this is what happened but nitrite poisoning seems the most likely to me.