I have to keep a high ph in my applesnail tank and after much trial and error this is what I have found works for me. The coral in the filter was such a small amount that it didn't really make a difference. I take a box of baking soda and spread it out on a cookie sheet and bake it for 1 hour at 300 degrees. add a small amt( less than 1/4 of a teaspoon to tank water in a cup and then slowly add about an ounce an hout to filter till the ph gets up to where you want it. If needed, you can add some when you do water changes but mine stays stable. I have a couple of handfuls of crushed coral mixed in my gravel. I also keep a large chunk of Texas Holy Rock or Florida Holy Rock in the tank, it disolves slowly and is appealing to the eye as a decoration. You can use coral heads as well. You can get the holy rock on ebay or pm me and I can put you in touch with the person I get mine from. good luck