They are glass tanks, thats part of the reason for all of the cracked tank threads on other boards. I used one of the small Twisters before I bought the Nimble and it worked out fine for me. The Nimble is quite a bit thinner though, it can even fit between the Hydor Deflector and the wall of the tank. Another thing that I have done to make it easier to clean my tank is that I cut the rim off of my Hydor with a sheetmetal nibbler, it did a very clean job and was quite easy to do. HTH, Skip