Theoretically many fish can be kept in aquaria "so long as extremes are avoided." That may be drifting a little low for the mollies though.

You can ask your municipal water department for the reports on water quality and contents which they are supposed to give the EPA every now and again. What is normally a boring list of figures becomes much more interesting when one gets into the basics of water chemistry for their fish. ;)

There are several things you can do to push the pH a little higher. It may be that your tap water comes out at around 7, but doesn't have a lot of the carbonates which buffer pH up. Perhaps just an increased number of partial water changes will do the trick and return your pH to 7 or 7.2. ("They" want the water to be a little alkaline or the lead pipes begin to leach into our drinking water.)

You can play with the pH changing chemicals, but that can be a little tricky. Depending upon what is needed, you could try a teaspoon of a Rift Lake cichlid salt per 7 gallons of water (about what is in a "10-gallon" tank). Measure after a day and see what gives.

If that works, every time you remove and add 2 gallons in a water change, include about .2 of a teaspoon of the Rift Lake salts. If that doesn't raise the pH enough, you could try a little larger quantity of the Rift Lake salts.

You could also put a tufa rock in the tank. They dissolve a lot of material into the water. Alternatively oyster shell grit could be put in the filter box. You also could try adding 1/4 teaspoon of baking soda at a time to the aquarium.

You don't want to overdo it. (A spawning fish is a happy fish.) One of the "tricks" involved in getting tetras to spawn is to add some demineralized water (rainwater, Reverse Osmosis water, the more expensive water run through ion exchange resins or the even more expesive distilled water) in order to trigger spawning in many tetras, dwarf cichlids or rainforest killifish.

As an example of how to do it all wrong, I had a pair of the rainforest killie, Aphyosemion striatum (the Christmas killie) in a tank of Lake Michigan water with a tufa rock. They were laying no eggs. Next to them, I had two (hopefully a pair) of the Lake Tanganyikan Julidochromis ornatus. There were no fry.

After a little reading, I moved that tufa rock to the Julie tank, which began to increase the hardness and pH of the water. In the killie tank, I did a removal of 20% of the water and verrrrrry gradually siphoned in rainwater (using knoted airlibe tubing for a siphon) to drop the hardness of the water. pH depends upon different minerals than DH or general hardness, but the rainwater has neither and biological processes (basically food digestion and excreted waste material and the bacterial breakdown of that material) began to drop the pH.

Within two weeks, the striatum were not only laying eggs, but laying fertile eggs. And the julies? The "two" somewhat differently sized siblings dug a cave under that rock and there was a small school of fry cruising the vicinity, also within a couple of weeks. :)

If your fish procreate in your tap water, don't fiddle with it except for weekly partial water changes. But if they are hurting or not procreating and you want fry, read up on their native waters, check your local chemistry and adjust accordingly.

Please let us know what you decide to do and how it comes out.