Hi. Currently, I have 2 tablespoons of crushed coral in my Top Fin Power 10 filter, which is being used for a 10-gallon tank with 3 adult male guppies and Cryptocoryne Wendtii in it. I put the crushed coral in when the filter was being used for a 5.5-gallon tank with the same water source and the same fish and the same Cryptocoryne Wendtii because I was having pH swings from 7.4 to 7.9 and back. 17 nights ago, the pH was somewhere from 7.4-7.6 (the API tests lose a lot of their accuracy in that range because one can only test up to 7.6, the other can only test down to 7.4, and they get less accurate at the extremes). Tonight, it was at 7.9. I don't want to add anything to my filter unnecessarily for fear that it will mess things up. I've heard here that adding a tablespoon of crushed coral at a time when having pH swings is pretty safe. But I think I only heard it from one person. What does everyone else think?