100ppm = 2meq/l = 5.6 dKH. My suggestion is to get a more reliable test kit or have a LFS verify your findings before trying to adjust Alk to normal levels(8dKH-11dKH). Could you please post your Calcium, SG and temp levels, one would expect to see your Ca low. You need to get your Ca/Alk levels balanced, if this is not possible then verify that your Mg level is within normal parameters ~1380 or ~3 times the calcium level(within reason). I use the Randy Holmes-Farley diy recipe http://tinyurl.com/3b4kdl for dosing these levels since I don't have a lot of sps. Here's another link for ready made packets of the diy recipes. http://tinyurl.com/2qruc7 . Make sure you read the dosing section also. HTH
Cheers!