I have two 420 gallon tanks with a drip system on both plus a large bead filters on each tank. I do a three quarter water change and backwash the filters every week.My problem is that I have a lot of fish and the PH is always low,I want to add crushed coral as to keep at 7.0 to 7.5 I plan to add a little crushed coral at a time till I get it where I want. I do not have any problems with ammonia but I have been told that higher Ph is better for holding oxygen when it is higher,and if the power goes out I hope it will buy me some more time till i get my generator going.please do not lecture me the about the fact that i am over stocked,that is my choice,so if any one knows any negative reason for not adding the coral please let me know. I know that tuffa rock would do the same thing but I do not like rocks because a lot of dirt settles under them,and in my tank with large fish I do not want them to smash into them if they get spooked thanks for your advice Noel