No need to mess around with your pH level. The best level pH for figure 8 is the amount coming out of your tap. Adding crushed coral to your filter does make the water pH and dKh fluctuate to higher levels after every water change, but these fish (and most other fishes) do better long-term with stable water parameters. Leaving your pH alone should keep your water more stable. Also crushed coral slowly lose effectiveness over time so you end up doing more work by measuring your levels with hobby test kits.
The only time I think raising pH/dKh with crushed coral is necessary is when those levels are too low out of the tap. When they are too low, then it affects the growth and sustainability of your beneficial bacteria and you end up loss all beneficial bacteria.
Edit: forgot to mention that certain fishes need high pH level to thrive, but figure 8 is not one of them.
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