I feel someone needs to jump in here. Some people have totally thrown the train off the tracks. The poor OP is seeking help, and some of these comments are anything but helpful. I for one would be very upset if I started a thread seeking help and it was high jacked by other members seeking a debate. For you that are into debating this and that please start a separate thread. Let's offer this person some useful help.
So in that vain... I personally would take a hard look at temp, and alk. If you alk is 10.5 when you test and I'm guessing your testing during the day. At night when your lights are out it will go up. This is one reason many people run refugiums on an opposing lighting schedule, it helps to stabilize alkalinity. 11 dkh is the high range and when you are testing your already walking the line. I would suggest to start check your alkalinity in the middle of the night, I'll bet you find that it is upward of 11 maybe more. You've got now padding built into your parameters to accommodate any fluctuations. Even with your temp too. IMO, drop those two (temp and alk) alk should be slow, and you will see more success.
Again please offer comments that will be helpful to the OP. Just my 2c