Nutrients, heat, flow, and just plain new tank are the main factors.

Crabs get rid of the visable, but not the problem. You still want lots of crabs and snails, but you also want to fix the problem.

Temps should be coming down some now on tanks without chillers as we head in to fall. Try feeding about 1/2 what you have been for a month or so. Clean your skimmer (big clean off the tank running vinegar through it for a few hours, rinse well, and put back) then clean the neck and cup every 3 days or so. Make sure there's no dead flow spots in tank.

For some reason it seems to be more prevelent in tanks under 1 year old.

Lastly, I personally feel Calurpa pulls more nutrients then cheato. It can also be a pain, but you might try some for a while and switch back to 100% cheato after you get things under control.

Todd