Instead of dipping a dendro, I like to carefully apply full strength 3% peroxide to the skeleton only, avoiding as much coral tissue as possible. I use a very small nozzle dropper & hold the colony or frag in such a way as the peroxide drips off away from the polyp area. And I make sure the polyps are fully closed & retracted inside before I start. I will brush frag plugs and lightly pick at the skeleton with the end of a soft crushed toothpick until all "fuzz"'is gone. Then it's a quick rinse & shake in a a cup of tank water and back in the DT or frag tank in a more suitable shaded location to hopefully prevent reoccurance.
This method works for me as it seems less stressful to tissue but does the job on the algae. The dendros may remain closed for a while but sometimes open quite quickly, ready to eat. They definitely responded better (for me) when compared to the results I got with dipping for several minutes. It's OK if you want to cut the full 3% solution by 2 or 3 until you're confident the corals can cope with the treatment. Use caution, YRMV.