Dec 07, 2006· That is my question to, how much crushed coral do you use and how much does it raise the ph. In my 30 gallon puffer tank I used 20 lbs and it raised my ph from up to which is great for a green spotted puffer, but I would not like it that high for tropical if I only used 10 lbs to my 30 gallon tank it would have only raised the ph by half the amount that it did.