You sure can. Most WalMarts sell RO
along with UV
treated for around $0.33 / gallon. Tap water is your problem. If the algae is a real problem, I'd drain some SW
and put everything in there except for fish, and then replace the entire amount of water with new SW
made with either RO
or distilled. That will knock your nitrates and phosphate down to around 0. You can also turn up your skimmer so it produces a wet skimmate instead of a dry foam. What kind of food are you feeding? Flake and pellet are loaded with phosphates. If you're using flake, I'd switch to a frozen food and rinse it real well with old SW
before feeding. Good luck!