GH at 200 ppm is equivalent to 11 dGH. This is moderately hard water. Livebearers would be OK in this water (the guppies are fine), but other species need more room. Livebearers also tend to be primarily upper water fish, which leaves the lower half of the tank empty of fish.
Fish suited to smaller tanks are termed nano fish. The unfortunate thing is there are more soft water nano species than harder water. The Glowlight Danio (Danio choprae) could work here, in a group of 9-10. I might find some others with some digging.
Be carefuyl with fish common names though. "Danio" generally are unsuited here because they are very active and need space. The Glowlight Danio is an exception on both counts.
Softening water is obviously possible, but it is a convoluted process, and you need to prepare the water outside the tank for every water change. Finding fish suited to the tap water parameters is always safer and easier.