yes, you can only dissolve about 2 tblsp in a gallon of water, if you add more, it will just remain at the bottom. The reactor will keep mixing the kalk every so many hours, so you'll be good.
As far as your ATO, isn't it on a float switch? Why do you need to regulate it at all?
If you must, then small amounts throughout the day is much better.
There is a risk, however, that you should be aware of. If something goes wrong with your ato, you can overdose on kalk. I, personally, am willing to take that risk. You can always user a controller to tell you ato to stop topping off if pH > x and alert you
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