Thought I'd post in this thread. I did get some of the product and wanted to let you know what happened.
BEFORE I do that, I wanted to say that since this thread I have noticed that Hoppy is much less participatory on APC. I wonder if his treatment in this thread had anything to do with it. I don't know. I would hate to think that members of APC are more concerned about "potential" harm to fish than kind treatment to a member of the forum. That seems a little out of kilter to me.
Now to my less-than-scientific results. On two separate occasions I took anubias out of my tank and put it in a bowl with 1 gallon of Prime treated water. Time #1 I sprinkled 1 and 1/2 tsp of Sodium Percarbonate. The anubias had some BBA and Green spot algae on it. I did this 2 times in about 2 hours. The product fizzed with fine bubbles. Afterwards I inspected the plant rinsed well with tap water and put it back in a fresh gallon of water overnight. In the am the plant appeared nice and clean, algae free. No damage what so ever. I stuck it back in my tank. No ill affects anywhere. I want you to know I WAY WAY OVER TREATED this plant OUTSIDE my tank. Never would I have put that much of this chemical inside my tank. I do think it kills algae.
Occasion #2. I used 1 gal of Prime treated water and again an infested anubias. It had green spot algae and a small amount of BBA. I again used WAY WAY too much, probably 5 tsp and sprinkled it on the plant. In a few hours I sprinkled more agian. I did this three times. Each time the product fizzed. The algae was dying. The next day I removed the plant, rinsed it well. I left it for another day in clean water. Then I put it back in my tank. The leaves began to disintegrate. The my shrimp (including CRS) swarmed all over it devouring the leaves. It became a mesh of leaf veins. I now only have the rhizome left. I am waiting to see if the rhizome will rot or if it will grow the leaves back. Obviously I reached critical mass with the chemical. NONE of my shrimp suffered any ill affects from eating the leaves. No dead bodies, no sick or slow shrimp. The fish in the tank are all very well. It's been about a week since I put this last plant (what's left of it) back in the tank.
Findings: This product does kill algae. You must use it sparingly. If you have a large area to treat do it little at a time. It will NOT harm fish or inverts that eat the plant treated with this product EVEN if the plant was killed. I would not hesitate to use it in the tank. I will use excel first for BBA. I will use this for clado or such that is harder to kill. I would also do the recommended water change 2 hours following treatment.