Cabomba is a finicky plant IME but it definitely appreciates more lighting than what you have. I've had little issues growing dwarf sags, wisteria, Ludwigia spp., etc. but again those aren't really the typical low light plants. I'm not one to just insist on a lighting upgrade as a quick fix, but if you want those species to be successful you may need to do so.
Can anybody link me to a 4 bulb 48in t8 fixture? I can't fit 2 of these fixtures unless I break off the two side things and glue em together. Needs to be from lowes or home depot