Be VERY careful when playing with the ph of your tank. Adjusting it too much one way or the other with chemicals will alter it too quickly, and this could kill your fish. If your mollys have been in your tank for awhile with no problems, I strongly recommend you leave the ph alone. Continually adjusting it is dangerous to your fish's health, and not necessary. I stand behind saying that unless you have an extra high or low ph, your fish should be find just the way your ph is without adjusting it. If you decide you do want to adjust the ph, be very careful, and add the adjuster slowly so you don't change it too quickly for your fish to adjust. There are also other natural things you can add to your tank to adjust it more naturally, like Texas holey rock to raise the ph, and peat or driftwood to lower it.From what I just looked at, you want your fish tank to have a pH between 7.0 and 8.0. Go out and get a pH tester, and if your pH is too low or too high you can go to the pet store and buy chemicals that will lower your pH or raise your pH depending on what is needed (if anything).