H2o2 is a great way to kill algae. My tank is small enough to do this, I drained almost all the water, spot treated all the bad spots, refilled with the water I drained them did a massive waterchange. For just rocks with no coral attached, you just just give them a ten minute peroxide bath. If there are corals attached you don't want to go stronger than a 50/50 peroxide saltwater mix. Zoas and sps are very tolerant of this kind of dip. Different results with LPS and leathers, so be cautious with those. Also, if you have a skunk cleaner shrimp setup a small qt for it as these shrimp almost never survive the treatment. Best part is after around 24 hours the peroxide just turns into oxygen so just drop the shrimp back in after a day.
Dosing directly to the DT is not as effective as the methods listed above. If you do decide to dose the DT don't exceed 1ml per ten gallons, you can SLOWLY up the dosage as everything gets used to it.
Also if you dip the rocks you will kill pods, but they'll repopulate.
Edit: Almost forgot, the highest DT dosage I've ever heard of was 4ml per ten gallons.