So, I last did a water change on Dec 19. My main tank was oddly high in Nitrate (40ppm) but I think it's because I just cleaned my canister filter and disturbed my bacteria colonies. My 5 gallon tank read basically 0 Nitrate.
I took about 80% of the water out of my 5 gallon and replaced it with the 40ppm water out of my main tank to see if maybe the handful of plants in the 5 gallon were soaking up the Nitrate.
It's been about 13 days and yep, reading about 5ppm nitrate on the 5G tank. (Only 20 on the main tank, yay) My marimos and ferns are looking very green! The teeny tiny pieces of fern in particular are looking much more robust.
Pleased to see also that my little rhabdocoela flatworms are visible again! I keep finding little drowned larva that I'm pretty sure are from moth flies. I get them in my main tank , but I almost never see an adult. I think my fish eat them when they pupate. In the smaller tank I think the water flow of the surface keeps pulling the larva into the water (they live at the water's edge, but drown if immersed)
They're both going to get a proper water change and cleaning when I get some stuff in the mail tomorrow!