They also make sheet roll that has release paper on the adhesive side so it's "Peel and stick"' I've had a piece of it blocking a couple weirs on an overflow that's a bit on the large side. I used the "Flextape to throttle the overflow basically. The tape has never moved or lost its bond and Coraline algae grows on it. Been up and running for 2 years and of the opinion its absolutely safe to use in your tank.