I would see if you can find the seaklear product at a local pool supply or phosfree and use RODI in a brute trash can and get it done before you start cycling. I am going to do this with the pukani rock for my next tank. But like I said, you might not have to. You might have gotten a good batch of rock.
For now I would pull the rock, rinse any dead matter/debris and dust etc off then put it in a brute can fill it with saltwater put a heater and a pump in it and let it sit for 2 days. Test for phosphates and go from there.