ph

Why would you want to change a neutral pH? A pH of 7.0 is perfect for 99% of fish out there!

And regardless of your pH, you shouldn't try to change it... even if it was 7.8, it is better to keep the pH where it is then to alter it. At the risk of sounding like a broken record, fish can handle most pH ranges - what they cannot handle is fluctuations. Even the smallest change in pH can throw the whole chemistry off. And this is considered very bad for a fish's health.

I'll second AquariumFishGuy… I wouldn't tamper with a pH of 7.

As to why it isn't moving… maybe you've got a bad test kit. Have you tried another kit? Your LFS should be able to confirm your results…

Its unlikely that pH would cause fins to disintegrate (unless of course... you're talking about a pretty acidic environment...). Water quality and/or the health of the fish is the most likely contributor. Most (if not all) mollies are raised in aquariums... many can do quite well in water with higher pH levels. Check your water parameters (ie. ammonia, nitrite, nitrates), and get back to us.

As the others have said, a stable pH is generally preferred over a "perfect" but unstable one. If you must lower pH, avoid additives such as pH down. Try putting peat in your filtration, or driftwood in your tank. RO water mixed with your tap water should also do the job.

-Richer

Mollies prefer more alkaline water so pH is certainly not why his fins have disintegrated. I would suspect poor water quality, as others have mentioned.