TLDR; Try Reef Brite's Reef Rock Enhance for a more natural & effective method. It worked for myself and I tried everything. H2O2 kills
everything, not just Dinos. Keep PO4 NO3 up and
balanced (P ~0.1 & N ~5-10).
Dinos will bloom when other organisms get starved out due to sub-optimal conditions and the good stuff dies off. That's when Dinos can thrive unchallenged. There's a constant microscopic battle going on in our tanks. It's our job to keep those conditions optimal for the good guys so they have a chance to prevail.
I personally feel the H2O2 is detrimental to the good stuff too as it's indiscriminate in what it kills. It may kill the Dinos but it also kills the "good" stuff so once you stop, the battle resumes and Dinos have a good change to come back. They did for me.
If you want to try something more natural I had excellent results with Reef Brite's Reef Rock Enhance. The stuff is like magic. lol I had Amphidinium, which is one of the more difficult to defeat, and I tried everything including high doses of H2O2, Vibrant, etc., etc.. RRE is what finally kicked it along with all the other uglies I was dealing with (brown crud, cyano).
Within a couple weeks my rocks and sand were clear and all the clogged up pores in the rock were clear and everything began to balance out. The normal green micro algae (and Diatoms from prior silicate dosing) started to appear on the sand & glass and everything looked so much happier (including me!

). It was funny how excited I was to see green stuff starting to grow in there. lol Dinos lingered in a few spots but eventually lost the battle and completely disappeared.
You'll want to watch nutrients closely and keep them up but
balanced (PO4 ~0.1 & NO3 ~5-10). Dose PO4 & NO3 if you need to but be careful not to get them too high because when the Dinos die back they can release some of their nutrients and you'll have a host of other issues like GHA. Don't let them get any lower either so the good stuff has a chance to regain the advantage. Keep the balance! Water changes will get them back down and back in balance if needed.
Good luck!