I found an acrylic-safe magnet that doesn't break the bank.

[Anonymous]

I got mine at http://www.marinedepot.com/a_mi_amc.asp?CartId=

This works well on my 55 gal. Two useful hints:

1. That red thing is NOT acrylic-safe and will scratch the bejesus out of your tank. It is removable. Remove it and throw it out. Don't even think of trying it like I did (fortunately on the back where it is obscure).

2. If you put a piece of paper towel on the outside under the magnet it also helps to prevent scratching and has the added advantage of letting you clean the inside and outside simultaneously.

 

[Jeff_S]

This company also makes these units for thicker acrylic. (models MM & RM) Has anyone seen any other than the blue model?