Uhhh, I just thought you would like to know:
Mollies are freshwater fish, not brackish.
What's this nonsense I speak?!?
Yes, mollies are freshwater fish that have a bad habit of swimming out to sea (literally) in brackish water tributaries. Just because you can find them in brackish water, doesn't mean you should keep them in it.
I am very well versed in molly keeping, and they thrive quite well in soft water with a pH of 6.4. They can also do very well in very alkaline waters. So what does this mean? Mollies are very adaptable fish! I speak from experience. I've put my mollies through hell and back (i.e., experiments, etc.) with very minimal losses; they are sheer troopers! They are amongst the hardiest fish I've ever kept.