hi new to the hobby n need help maintaining water parameters

can anyone help me i have a 30 gl innovative marine tank sump is in the back i have ghost skimmer and a bio pellet reactor i just added 2 days ago.... i been having this tank for about 8 months just started to introduce coral i have a hammer and a xenia..... my problem is my ph level is about 7 n my alcalinity n calcium and magnesium have been dropping for some reason anyone have a solution plz thanks dont want to have my corals dying