Hey kwheeler! Long time no see! I haven't been around much either over the past few months, myself. No worries!
Selaginella species commonly grow in very humid and moist terrarium or vivarium setup. I have a few that are hardening to conditions around my cool mist humidifier right now that I will take pictures of. All of them are terrestrial species, as far as I know, EXCEPT for this one, which will start to die completely once it is about an inch from water. It will grow a little emergent, but even the tops will dry out once it grows out from the waterline. So, this is almost certainly an aquatic species. It prefers to be submersed.
It doesn't seem to attach easily to driftwood or stone. I learned that the trick is to grow this on top of moss that has been wrapped around a branch. Under bright light light, the moss seems to survive alright, even as the Selaginella quickly covers it as it grows. This species really seems to thrive in my high light and pressurized CO2 system. It probably would do fine with average kH, even though my kH is probably really low. PH is slightly acidic in my tank, so neutral values are tolerable. It needs good flow in order to keep debris from clinging to the leaves. Otherwise, normal ferts are fine. The limiting factor probably is the lighting. I do not think that this plant would do really well under weak lighting.