Black Spots on Angraecum - Please Help!

[HiOrcDen]

I have a very large Angraecum which started developing very small black spots, surrounded in yellow, soon after I purchased it. I thought this was a sign of sunburn. Though my lower light requirement plants were doing fine in the same level of shade, I thought these spots may have come from a small gap by the shade cloth, or perhaps this plant being too close to a wall.

My Orchids are temporarily inside, with full spectrum lights, near an open north-facing window, for fresh air. The weather is moderate. The spots had stopped accumulating, for a good while, but now the Angraecum has developed a few more. They are all on leaves halfway down or lower. I have researched on the web, and if not sunburn, I understand it might be a fungus or a bacteria. I have taken measures to make sure there is good air circulation and drainage.

How will I know if things are too far gone to the point of needing to check for and clip rotted roots, or cut out spots?

I have something called Bio Advanced 3 in 1, in a spray bottle. Is this okay for an orchid, and could it help? I've also read that hydrogen peroxide may help. Should I apply either or both of these? Is there another product specifically for orchids which will work well? And if I buy it, again, should I use the hydrogen peroxide (in which case at what concentration) or Bio Advanced 3 in 1 in the meantime?