Dont know if this is in the right place but im having a bubble algae problem thats getting very hard to deal with i mean how many emralds can one have lol...
You could put a few in there. I would probably do 3-4 and see how that goes. Once the algae is under control you can remove a couple so they don't have to fight for fewer resources.
How long have the emeralds been in? Every time I have had bubble algae I toss an emerald in and it's gone within a couple days. It usually takes a little while for them to find it unless you put them right on it or you have it everywhere, which seems to be the issue here. Have you ever seem them picking at it? You may have to check a few hours after the lights have gone out.
Emerald Crabs most definitely are hit or miss. Not all will eat Bubble algae. More times then not they'll become part of the problem and not a solution. Seems so in your case. They may be eating yet breaking the bubbles while doing so, thus releasing the spores.