Ya, I didn't think it would be the fertilizers. I may have just figured out my problem them. I have gone through so many options and scenarios that I feel like a detective. Anyway, I have been using water from our kitchen faucet for water changes, the only faucet in the house that isn't hooked up to our water softener. Anyways, it is freezing here and the tap water is about 55 degress and I've been using the hot water to bring the water to room temp quicker. Well, the water heater comes AFTER the water softener and I've been getting all those wonderful chemicals and such that come from the softening salt. Does this make any sense? Could the water from a water softener cause algae?