What are you feeding the tank? The flake foods are very high in phos. The frozen should be strained before adding to the tank (brine shrimp net would be perfect). I would remove 1/3 of the rock weekly into a bucket that's kept moving, but dark. Start feeding one or two times per week at most. And you may want to do a couple weeks of fresh ground seafoods just to ensure that there's no PO4
getting into the water.
If you're testing .2 then you're off the charts for what isn't being consumed by the GHA. You have to find the source of the PO4
(what kind of food? what kind of salt? what are the readings of a fresh batch of your RO
? Salt mixed water?) in order to get it under control. Everything else is just a "clean up" process and doesn't really work until you've eliminated the source.
has great prices on inverts. Our club is doing a group buy right now so we'll all split the shipping. You need to order at least 100$ so maybe that isn't the answer if you're looking for a cheap answer.
At long last, look into dosing Vodka into the tank. I've heard that it causes a chain reaction (of drunk fish, lol) that causes bacteria to out compete the GHA and blah blah blah the next thing you know no GHA.
Good luck. Hang in there!