There is an interesting, thorough article in this quarter's Orchid Digest about Boisduval Scale. I was surprised to read, "(Quaternary ammonium chloride solutions show)...there is some effectiveness on scale crawlers and other delicate insects. Quaternary ammonum chlorides also seem to mix well with most insecticides and fertilizers, functioning as a surfactant." I have been using 20% pool algicide (which I understand to be a Quat) as a lightweight anti-fungal, anti-bacterial agent for years, mixed with my fertilizer at weekly applications. I find it interesting that this may have been helping me control scale, too, all along. I have never experienced any signs of toxicity, and I rarely have fungal problems, despite keeping my shadehouse very wet. Therefore, I think there is some benefit to using the algicide. Thoughts?