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I've always had trouble getting suction cups to stay attached above and below water...any hints and tricks I might be able to use?

I think it depends on the actual suction cup. I couldn't get the dock to stay (my goodness..that was like 10 years ago.. my turtles are too big for that little thing now!). I bought a pack of 10 at the dollar store and they are the best ones I have seen!

Make sure you clean them - they have a tendency to have slime build up. The stiffer ones also seem to lose their shape (and effectiveness) more often.

For your heater they sell magnets to hold it.

http://www.fosterandsmithaquatics.com/p ... atid=19711

Ok, should I clean the place where they stay well too?

Yes, try to keep it as clean as possible.