Tetras and barbs, really most fish in general will love your water, but unfortunately the fish you currently have are some of the few that will not tolerate it. Livebearers need higher ph levels and hard alkaline water to thrive or they won't last long.im just curious does anyone know what kind of fish would be suitable for low ph between 6.0-7.0 ive tried to raise my ph but it still goes back to between 6.0-7.0 and right now i have a molly, a platy and a guppy in a ten gallon tank