I had a similar issue with Salifert, except mine was with an Alk kit.. The test was reading 4.6 dkh so I dosed accordingly to get it back up to 9-10 dkh. By the time I finally got it up to 9 my coral started to bleach. I purchased another Alk kit from Louis and sure enough the new kit was reading over 15 dkh. I learned my lesson, I now keep multiple kits with different exp. dates.