[DJRansome]

Any shells will help with buffering. But I would not buy aragonite substrate, if I wanted something I would buy crushed coral for the filters.

 

[DJRansome]

Crushed coral does the same job for a tenth the price and minerals dissolve better in the filter with the water flowing over the material.

I have a lot of aragonite substrate and have had it for over 10 years, it was my first substrate. I like the much cheaper and easier to maintain pool filter sand better.