I try not to mess around with the Ph to much, chemically that is. So i dont know if you can do much about it. cause if your water suply has a low Ph. As soon as you do a water change its going to change again. Also having a smaller tank is harder to keep the ph and ammonia levels down cause of the such small water volume. If you say 6.0 ph what seems about nutral if i remember. That sounds Fine to me. Actualy that sound quite nice depending on what your fish prefer.