UG filter in my turtle tank

Question
I just bought a Perfect-a-flow undergravel filter for my 20 gallon long tank, and it sits under about 2 inches of course gravel.  I have a Topfin 20 gallon air pump attached to my setup.  Ever since I installed the filter and pump yesterday, a small bit of water has been going up the tube like it is supposed to, but most of the tube is filled with bubbles.  No water is making it up out of the tube and back into the tank like it is supposed to.

Answer
UGFs are completely useless.

They can actually hurt your tank by ruining a cycle, it would be better in some cases to not even have one.

I would add a Aquaclear 50 HOB instead. You can get one for $30 and it will be 1000X better than any UGF.

Leave the HOB in the tank for about a month to collect bacteria and then just take the UGF right out, but trying not to disturb the gravel TOO much.

Oh, and contrary to the label on the AC HOB, you only need to replace the sponge every 6 months and the bio max every 18 months providing you rinse it out every month or so.