Yes, you can add coral chips. My Tap water PH is already around 8 to 8.2 most of the time. I put around 500g of coral chips for a 50 gallon tank is just nice for me to buffer the PH to always remain at 8.2. You need to measure the PH to make sure it does not exceed 8.2 as well after adding the coral chips. Last i put 1kg of coral chips thinking more is good for my 50 gallon, the PH increases till 8.5, my kamfa head keep shrinking and colour fading until I reduce the Coral chips to 500g and did a 90% water change to bring the PH back to around the 8 to 8.2 range. I find that long as your PH is between 7.5 to 8.2 and don't keep fluctuating, flowerhorn will look at their best.