ATS are great and I used one for a few years. If a skimmer and ats were my only options I would use the ATS. I still have a clearwater setting on my shelf in case my new setup needs additional help. You will not see much of a ph difference compared to a skimmer. You might see a slight improvement. The algae has direct access to the co2 in the air and that gives an ATS an advantage over a refugium for nutriet export. I use a refugium over an ATS for other reasons. I would definitely do an icp test within a month and a second 2 months later. It will remove minerals that your corals need. Specifically magnesium, lithium, manganese, iron, and iodine. The second test will give you a baseline of mineral consumption. Then you will know how much you need to add. You may find that the other things you are adding are replacing the minerals at an acceptable level. Water changes, 2 part , kalk, food, etc. I would rather know than not know.
When I was using mine I scraped one side and left the other. Then alternated scraping one side each time. This may not have been needed but as my wife says I have to over engineer everything. This was not needed but I felt it would give the system more consistency. From memory I waited until the screen was full of thick GHA before scraping it. Probably 3/4 to 1 inch thick.
