>>508032996They haven't used direct nutrient tanks in the industry (at least in the West and China) for years at this point. Keep the fertilizer solid until you add it via concentrate injectors. There's plenty of other stuff that can break down, but algae alone is not a serious issue.
As for microbes in your water, there's 2 competing philosophies:
1. use stringent treatments and filtration to keep the water clean . Also don't keep too much water stored at any given time, pull upon your reserves as you need it. (sterile approach)
2. Inundate the water with massive amounts of harmless or even beneficial microbes for your crop so that they outcompete any harmful growths while also enhancing or at least preserving the water quality.
There's a lot of other issues, like the fertilizer chemicals either being bioweapons or requiring massive amounts of energy and infrastructure to create in meaingful quantities, but it's all stuff that's been proven to various degrees by both hobbyists and professionals.