How long does this take to take effect? Will raising the temperature help?
Raising temp causes the lifecycle to complete faster. Have you seen any reduction in spots at all? I'm not sure that's a good idea if you haven't, it might just make the infection worse.
I'm not sure how good this stuff really is for whitespot, i know it helps with velvet but not sure on ich.
If you can't get the fish out, you might want to look at plumbing a UV system in. Doesn't get rid of ich but keeps numbers low enough that the fish can fight it off.