So I added a Reef Octopus Kalkwasser reactor. I programmed my apex to stir every 2 hours for 5 minutes. And I hooked my ato up to reactor. Setup was pretty easy. It seems to be doing a good job keeping up with calcium and alkalinity. Also I'm actually getting to 8.4pH during the peak. For those that have walked this road before, how often should I test magnesium? Also, I still plan to add calcium reactor once this doesn't meet demand. Or would it be better to add now and run a higher pH on effluent?
I like to check Mg at least every couple of weeks, though I sometimes don't. If Kalkwasser is giving you a stable Alkalinity where you want it, I would just wait till it's not adequate to do the job. You already have spent the money on it, might as well ride that horse as long as it's viable!