Would love some with fish stocking recommendations in an established moderately planted 20 gallon. We've got 5 Kuhlis, 7 Ember Tetras (bought 10 and should have counted them before leaving the store ...), ~ 10 RCS and 4 mystery snails. With the current fish/invert load nitrate and nitrites are 0 even with regular fert dosing. Eventually will add a long-tailed Betta (last) but in the meantime wondering if we should add more Embers (they aren't coloring up as well as I'd like and we've had them for a month) vs a handful ~ 5-6 of Harlequins given their shared natural habitat with bettas. Thanks for advice.