MissOrchidGirl uses 3% and she won't go any higher than that.

Also, I was just scolded for putting 3% H2O2 on a rotted cattleya on another orchid forum.

How are your plants doing?

Thanks for your answer.

It's been 2 months and well it appears that I did bleach the poor things. I had seen that 10% could be used to burn resiliant pests in orchids and 5% was for general use/watering. So 6% was on the safe side, but the safe side of an unsafe advice. I will not go above 3% from now on.

As for the plants, for all of them I removed the dead roots, replaced the sphagnum moss (which was degrading) and kept them in cool (60-70F) humid atmospher. The Dracula Rezekiana (who at the time was about to flower) handled the bleaching better than the other (but of course the flower stems dried up and no flower develloped) and seems to be recovering and just today I spotted a new leaf starting to bud in an otherwise almost dead looking Dracula Simia (just two dark green dry looking curled leafs). Unfortunatly the Dracula Saulii and Masdevallia Caudata and Glandulosaa are probably gone. It will take a long time but I might be able to get some of the plants back. In the mean time I'll wait for the Habenaria Radiata to sprout.

H2O2 is very unstable and many commercial preparations have additives to prevent breakdown. I don't know what the added compounds are but I wonder whether they might be detrimental to sensitive plants.