I do a 20g a week change on my tank and have used the Red Sea Pro for over a year now. No issues.
You have to add it slowly as Chris and Alton said. I am using approximately 1/2 cup per gallon and that gets me close. I add 2 cups at a time and wait for the water to clear up before adding more. I mix the water a day before using it - so if I know I want to do my water change tomorrow night I will set everything up tonight to mix. One key I have found that helps me is strong pumps to mix and using aeration, I use 2 older Koralia 4s in a 32g Brute can. I use clean water and vinegar every other month to clean the pumps and mixing container because you will get a little residue that builds up.
One other thing that I do is test the new water prior to adding it to the tank to check params. I have not had the issues of low kalk yet though.
John
"Critics are men who watch a battle from a high place and then come down and shoot the survivors." Ernest Hemingway