Over the past week or so i have been having trouble keeping the PH in my african cichlid tank where it should be. I try to keep it at about 8.2 - 8.4. I use crushed coral in the filter and i have two fairly large calcium rocks in the tank. It is a 30 gallon tank. The PH has fallen to about 7.8-8.0 is this because the coral in the filter and the rocks are no longer producing enough calcium to keep the PH up??? The rocks are only about 3 weeks old and i put the coral in the filter at the same time?? Do you think i should get another rock or use more coral in the filter?? Or both??