New to ats

[Supra]

Hey all, just to give you a heads up, I got half way through the reef sanctuary thread then found use here. Ive read the fact section and some other stickies on hear. I'm getting to set up 125 w/ 55 sump and 20 return. I have a protein skimmer I bought used off Craig's list (asm g3). After doing the research on ats I was gonna hold off on skimmer and go strictly ats. What do you think? Also with little water changes I'm assuming I would have to run kalk? Also how do inverts and snails hold up in these systems. That's it for now and thanks for all the research you guys do.
Supra

[SantaMonica]

Don't need or want the skimmer with a reef. Will have more food for the inverts and corals. Yes kalk or some other way to add Ca and Alk.