Hi. I would like to change from a crushed coral substrate to aragonite reef sand because of two things. AA tells me it collects food and waste faster than sand. Also, I will want to add blennies in the future I just love their faces. I now have 4 chromis, 2 stars and 2 snails. Do I replace the old cc all at once or do something like 1/3, 1/3, 1/3 and can a siphon do the work or do I shovel it out while doing a huge water change? I appreciate any and all help.