I have a fluval 304 in a 20 gallon and running no skimmer and the water if crystal clear, no problems what so ever with the water. But, on my 80 gallon I run a fluval 404, skimmer Prizm, uv sterlizer, 2 power heads and the water if cloudy and I have a phosphate problem and currently have an alge bloom.
And the both take the same distilled water.