Hay wanted to reply this morning had to go to work. The PVC pipe under gravel should work with sand. I have never had a full sand base tank, I usually use gravel for a 30mm base then coat the top with sand, this allows water to flow more easily through the base, then any under gravel will work.I still use UGF in one of my tanks and they do work very good. I had it also in my 55 gallon tetra tank until I switch from gravel to sand. As long as you do a good vacuuming of the gravel ever so often. My LFS also uses UGF in all his tanks for years. Sand will not work with a UGF unless you have something to keep the sand from falling through the filter plates openings. You need the space under the plates to draw water through to the up lift tubes and with sand it will fill up that space and shut down the filter.
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