LoneStar

Just be aware when using new razor blades, a lot of manufactures coat the blades in oil to prevent them from rusting. I'd wash them in water and make sure all the oil is removed before using them in your tank. Otherwise you can't beat using them for scrapping algea off the glass.

I second the idea of using liquid teflon instead. Teflon tape was invented to be more of a lubricant than a sealant when applied to threads on pipes. When used on PVC pipes, you do not get a 100% sealant. Using liquid teflon as a thread sealant works far better and when applied right, will not leak