I've never had a problem with green algal growth on my orchid leaves until I began growing in my new controlled growing environment. When I first saw algae forming last spring, I thought "wow, how cool". After while however, I began to wonder if the algae was doing more than just hitching a ride on leaf surfaces. Despite continued algal growth, my plants seem to be growing fine, so I figured that the coating wasn't detrimental to the health of my orchids. At last month's San Francisco Orchid Society meeting, Marni Turkel and Judy Carney taught a great skill session on grooming and preparing plants for display at shows. It was excellent, and I was inspired to clean the algae of of the leaves of some of my plants that are in spike. Last week I picked up some 3.0% H2O2 and loaded up my sprayer. I drenched my plants in it and watched everything fizz and hiss. After a few minutes I sprayed water on them to wash off the dead algae, however not all of it came off. In the skill session it was recommended to wipe the surfaces of the leaves with paper towels, but most of my plants are angraecoids and I get nervous about bruising (or breaking!) the leaves because of clumsiness. Also the leaf axils are hard to clean with a paper towel or tissue. Yesterday I got back to working on cleaning with the leaves, this time with fine paint brushes. It takes longer, but it works very well! It's a curious feeling to be painting the leaves of one's plants, rather Zen. I do wish I would have cleaned the algae much sooner. A number of leaves that had thick coats of algae for 8-9 months are now mottled because they weren't able to photosynthesise properly or evenly. This mottling distracts from the aesthetic beauty of the leaves. I don't recommend procrastinating algae removal. Some commercial growers include diluted H2O2 in their water lines to keep algae from ever forming. In the future I may try adding a few mL to my tank each time I water. Apparently some Dendrobium spp., especially nigrohirsute species are sensitive to H2O2 and will defoliate when sprayed. I am interested in hearing how others control their algae.