I Have a 55 Gallon tank and am kind of new to the whole fish keeping thing. I keep my PH at 7.9 and temp at 74-76. I have 8 freshwater clams (About the size of top necks) and two fiddler crabs (male and female). What I am looking to find out is can I add anything like calcium to the water to help healthy growth of the clams and crabs without affecting the PH and health of the other fish; Or should I leave well enough alone? Thanks in advance for any help!