Backyard Aquaponics
A place to discuss aquaponics

Any thoughts would be appreciated. I have a 3000 litre, 5 bed system from BYAP with 125 Silver Perch. The system is 18 months old and have only had the occasional death in 18 months. Over the last 36 hours I have lost 13 fish, and 2 weeks ago I lost 2 fish. The dead fish size ranges from 80 gm to 550 gm. The pH is 6.6, Ammonia is , Nitrites are 0, Nitrates are . The water is perfectly clear.
Two things have happened recently
1) It rained for the first time in 3 or more months 2 weeks ago (only light rain) and then heavily 3 days ago. The fish tanks and grow beds are covered with 50% shade cloth. Immediately behind us, there is new house building - 3 separate houses within 50 metres.
2) 3 weeks ago, the fish were the hungriest I have ever seen them and I pulled out the tomatoes. I checked water daily as I wondered if removing 2 beds of tomatoes would be a problem (new seedlings planted though). The ammonia did rise for a few days but never higher than , the nitrates never registered above 0 but the nitrates went extremely high - very dark red for a full 10 days. We almost stopped feeding for this time period and by the time the deaths occurred, the ammonia has disappeared and the nitrates are down to

I am wondering if some building toxin has got into air and then rain has washed it off shade sails into the system. The dead fish look perfectly normal with no signs of fungus. All the other fish are swimming very slowly and not interested in food. I have changed the water by 30%. Any other ideas? I have not used any toxin in my garden - only insecticides have been Dipel and two applications of Neem oil on 4 eggplants (eggplant caterpillar) only (very light application using about 1/4 ml in 100 mls spray.)

My apologies. I am a newbie at this. My system of giving test results didn't work. I will report this with numbers inserted instead.
Any thoughts would be appreciated. I have a 3000 litre, 5 bed system from BYAP with 125 Silver Perch. The system is 18 months old and have only had the occasional death in 18 months. Over the last 36 hours I have lost 13 fish, and 2 weeks ago I lost 2 fish. The dead fish size ranges from 80 gm to 550 gm. The pH is 6.6, Ammonia is 0 ppm, Nitrites are 0, Nitrates are 20. The water is perfectly clear.
Two things have happened recently
1) It rained for the first time in 3 or more months 2 weeks ago (only light rain) and then heavily 3 days ago. The fish tanks and grow beds are covered with 50% shade cloth. Immediately behind us, there is new house building - 3 separate houses within 50 metres.
2) 3 weeks ago, the fish were the hungriest I have ever seen them and I pulled out the tomatoes. I checked water daily as I wondered if removing 2 beds of tomatoes would be a problem (new seedlings planted though). The ammonia did rise for a few days but never higher than 0.5 ppm, the nitrites never registered above 0 but the nitrates went extremely high - very dark red (160 ppm) for a full 10 days. We almost stopped feeding for this time period and by the time the deaths occurred, the ammonia has disappeared and the nitrates are down to 20

I am wondering if some building toxin has got into air and then rain has washed it off shade sails into the system. The dead fish look perfectly normal with no signs of fungus. All the other fish are swimming very slowly and not interested in food. I have changed the water by 30%. Any other ideas? I have not used any toxin in my garden - only insecticides have been Dipel and two applications of Neem oil on 4 eggplants (eggplant caterpillar) only (very light application using about 1/4 ml in 100 mls spray.)

It does sound a bit like something could have washed off into the tank.. Also I would suggest that if you have fish that are about 500g you might want to start harvesting some.

This does seem to be quite a common scenario with the first decent rains. A few years ago I lost heaps of Silver Perch when one of my tanks was just hanging out from the eaves and we got our first good rains. I have had customers lose fish in similar circumstances when rain water enters tanks from roofs or passing through timber and shadecloth. Im not sure what the cause is but suspect it may have something to do with the accumulation of dust particles over the long dry summer months and the fact that your system is next door to a building site I imagine your shadecloth would have gotten quite dirty over the last few months.

Fish can be such pathetic wooses sometimes..

Seems like several water changes are in order until the fish aren't stressed anymore. So during a long dry spell it might be beneficial to clean the shade cloth several times or maybe even erect the shade cloth at an angle so during a rain, the water doesn't drain in the beds/tanks. Might be better to put some sort of plastic sheeting under the shade cloth. Guess this would be a +1 for greenhouses.

Many thanks everyone. Deaths have stopped and fish are active again. I assume it was a very fine dust blocking their gills although the water remained crystal clear to my eyes.