I use old credit cards. The edge is just sharp enough, it won't rust or cut you, their free and will last just long enough for the next one to expire and need replacement. As long as you have credit you have an endless supply. And no high nitrates will not cause a coralline algae bloom. If you keep your water parameters SG, PH, Alk and Ca in line for most hard corals your coralline will spread.
[ September 13, 2001: Message edited by: DAN THE MAN ]