I changed my skimmer bout six months ago. Nothing new to the system. I checked the PH right away, thinking that something had gone south, Ph reading was 8.2. If the Ph keeps constant so will the Alk. I did'nt check Cal, because I dose daily keeping the Cal above 400. The ASM payed for its self many times over, that evening. Tanks doing fine. I wish I could say the same for my 480gal, can only keep softies for now.