I'm using 2 of the exact same ones on my 75 gallon with Fluval 304 filters and they work great. My tap water seems to develop a film on it. I thought at one time that I had gotten something in my tanks but later found that just a bucket of clean tap water will film over in about 3 days. Anyway, they keep the surface completely clear of any film and will also pull in any floating debris like leaves.