..
In attempting to find reasons for fish deaths, I had cast my mind back to ANYTHING that I had done around the system.
One event I recalled was spraying thrip with ECO-Neem.. A so called safe and organic spray pesticide..
Yes I was careful, but I could not guarantee NO DRIPS or overspray..
anyway..
I wrote to the ECO people and asked about product safety with Aquaculture, and though it might be worth sharing, if it was not obvious to others..
Quote:
Hi Peter
Unfortunately eco-neem can be toxic to some fish and if your fish died very close to a spray treatment then it is probably the reason.
In general we do not recommend using it around fish for this reason.
Eco-neem is made entirely from plant oils/extracts which are broken down by the usual things eg sunlight, temperature and bacteria. The active insecticidal components in eco-neem start to degrade quite quickly when it is diluted into the spraying solution unlike many other insecticides which stay stable for several days. When sprayed onto plants any residual solution on soil, in water etc... will degrade even faster due to the presence of bacteria. This means it's good news in your situation as the neem won't be hanging around for ages to harm future fish. How quickly it dissipates will depend on various factors relating to your water quality and setup. To be extra cautious I'd leave it a week and then introduce a couple of fish as "guinea pigs" as a test.
I hope that helps.
Steve
So, I do doubt that this was a cause but I will never know...
bottom line - ECO does not mean SAFE...

when dealing with fish..
Everything should be treated suspiciously around fush..
and... my thanks to Steve, who I hope won't mind reproducing the honest comments..
..
.