Hi, everyone - I have a 20 gallon tank with 6 glofish tetras (skirt tetras). Parameters are all fine 0 ammonia and nitrite, nitrates under 20. Not planted (silk plants but I do have some moss balls in there), weekly water changes 25 - 30% with gravel vac, GH 2, KH 6, pH 7.6, temp 77. The tank...