I was hoping there was a chlorine/bleach type product i could add to the res on a regular basis to keep things in check, im running out of things to try!
Then I think chlorine dioxide might be your best bet - I don't know enough about it to be of much help, other than I was told that's that what a lot of the commercial hydroponics industry uses, added in small continuous amounts, to keep diseases at bay. And at significantly higher temps (say in a greenhouse) than you're probably keeping your reservoir at.