I have 2 20G and both are cycled. The nitrates NEVER really get to 5ppm. They come close, but never get there. I let it go 10 days between WC this week because of school stuff and my husband being out of town. One tank (the original) especially isn't getting much nitrates. In that one we have 1 male betta, 3 platies, 2 otos, and 1 kuhli loach. It's got 2 large amazon swords, 2 good size bunches of water wisteria, a good bit of java moss, 3 anubias, and 1 large moneywort. Should we get some more residents? Before we added all these new plants, about 6 weeks ago, the nitrates would rise steadily up to about 10-20pm.
The other is a 20G sorority, with 7 bettas, 6 mollies (3 being 4 month old juveniles that I'm trying to rehome) and I suspect a few snails (I know I saw at least 1). It has 2 reaaaally large amazon swords, with several runners (4 I think), 4 small amazon swords, 3 small anubias, good bit of java moss, 1 umbrella plant, some ludwigia, some water wisteria, and a medium-sized cryptocoryne. ETA- oh, and one small bit of telanthera? cardinalis and a java fern.
I still do my weekly WC, but I keep it to just 25%. What would be best?