Now youve tested your ph and that it is 8.0 you dont need to worry about raising it, its high enough. This also means you havent really got to play with your gh and kh.
If your ph was low say 7.2, but your gh and kh were high, you could sacrifice the lower ph and be fine. As you have a high ph then i wouldnt really worry about it.
As for putting the crushed coral in your filter, i would prob leave that aswell, you would have better having coral sand in the tank but then again your ph is high so doesnt really matter. If you did want to raise the kh then baking soda is easy to use. It will raise your ph aswell but it will max out at 8.2.
Id also put more rocks in the tank. Cheers