diablo30xp

my alk constumption high...I tested my alk a day ago and it was at 7 dkh...I added the amount needed in 2 days to bring to 9kh cuz I split it...well I tested this morning and it was back own at 7...I have a 108 gals al together 93 gal cube plus sump...I about 20 sps frags and a couple of lps and a clam and rbta....would this b accurate the amount being consumed or something im missing??