H2O2 dosing in the DT is possible. However, it depends on what corals you have. H2O2 dosing is also ONLY a temporary fix, keep your water params in check to properly control GHA. I was dosing H2O2 straight-up with a baster on my LR, it was a last resort for me as none of the corals, clams could be removed without harm. It WORKS, however keep in mind that it will only be a temporary quick fix. I can tell you that it is safe for all fish and inverts, but be warned that there are a few corals that won't tolerate H2O2. Open Brains are one of them, as well as Xenia's. I would also assume quite a few softies don't tolerate H2O2 also, I don't have any softies in my tank so I can't tell you in detail.
H2O2 also works well against Cyano. My one piece of advice is to dose your DT, wait 15 mins or so for the H2O2 to work, and then do an immediate WC. You will find that the fish appreciate the extra oxygen in the tank, and your CUC will work a little over-time and feast on the easier to digest oxidized GHA.
Here is some good reading on tank-wide dosing if anyone's interested.
http://www.nano-reef.com/forums/inde...owtopic=268706