what is you ph without buffering?

I often use crushed coral or aragonite sand as substrate to keep the ph buffered but I don't usually measure it out (just cover the bottom).
I have met a few people who place the crushed coral in filter bags and use what appears to be 3 or 4 cups in a 55g...

but, as you said, it will take some trial and error to find out how much is needed for your water

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Gold Coast Aquarium Society South Florida