To those of you that think a little pesticide is OK to the environment, even 'environmentally friendly' or 'organic' pesticides *can* kill fish. And it soaks in many skins of veggies/fruits.
Even organic farmers cannot be trusted. You must go aquaponics. It's like a canary in a coal mine. If the fish die, something is wrong.
Organic farms are legally allowed to use pesticides in most countries, if not all of them. They are just limited to the amount they use and the times they use them.
This is also a warning to people who want to grow aquaponics in containers that once held 'organic pesticides' as well:
There have been toxic results with totes used to store propionic acid (a food preservative that is used in animal food processing); and totes in which organophosphate insecticides or herbicides were stored or mixed "for a short time only".
Citric Acid: This is an organically-approved herbicide, and you can spray it around your system by using extreme care. But don't spray it onto your vegetables, or use it to adjust pH downwards in your system; for it will turn your plant roots black and kill them all. It's an herbicide.
"Organically Approved" Oil-based, Pepper-based, and Soap-based Sprays:These are all toxic to the fish through various mechanisms. The oil from the oil-based sprays ends up coating the gills of fish, and their gills stop working or work so poorly that they asphyxiate. The pepper from the pepper-based sprays goes straight into the fish's bloodstream through their gills (just like you getting pepper spray or Mace in your face: people have died from this), and this kills fish. The mechanism by which the soap-based sprays works is the same as the oil sprays: soap is half oil and half water, and the oil fraction of the soap coats the fish's gills and they asphyxiate.
A student who had his entire operation inside a greenhouse sprayed his vegetables, very carefully, with a soap-based spray. His rationale was that since he was careful, and since there was never any rain inside his greenhouse to wash the soap spray down onto the rafts and into the water, he would be safe. It took him several spray applications over a three month period, but he finally killed all 800 pounds of fish in his system.
Mildewcide and Others: It's a toxin that is designed to be added to paint to kill any mildews or molds that might be tempted to grow on the surface of your house. Using it on a raft will introduce the same toxin to everything in your system. Another example: If an upwind neighbor sprays an organophosphate insecticide or herbicide, a miniscule amount of this stuff washing into your water can kill things in your system.