at those levels, I can't see any reason there would be precipitation assuming you aren't trying to add too much at once. I dose, maybe a couple times a day, to get where I want to be and then make sure the CA reactor is keeping it there. I had to shut my reactor off for a while and without it, I could not maintain my levels. I would dose Alk up to 10.5 before I went to bed and it would be at 8 in the morning. These tanks use up CA and Alk real quick if you have coralline and SPS. You might post in the reef chemistry forum or look around it a bit as it covers Alk and CA all the time. Just FYI- I have a Korallin 1502 and it just barely keeps up with my tank. I am planning on getting a bigger unit. I'm going with a Geo 624 which seems like a good deal for $400.