how many crays do you have? i also have a ton of algae in my 10 gallon cray tank, but i dont scrape it off cause im waiting for april POTM. you can use a razorblade to get it off if you want, but you still need to figure out why its there. what and how much are you feeding? whats the wattage on the lights? how long do you leave the lights on? what are your parameters?