I got one of these to hold my lamp i didn't want to clamp onto the top of the terrarium http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

My lamp had a clamp on it that I just hung from this thing.

Depending on the filter it will need between 2 and 4 inches of water. It could be that it just want getting enough water flow to it to work properly.