I've been using ATI Essentials since, roughly July-ish, but I have a very small amount of corals, actually just 1 coral, so my dosing amount is very small, 8ml of part 1 and 2. Part 3 is on hold as for some reason my pump dumped 500ml into the tank, and if that was going to happen, I'm glad it happened with part 3, and not part 1...but we're close to part 1 and 2 being at the level of part 3, and once that happens, will start dosing all 3 in equal parts again.
I recently changed my lighting from LED to a 6x80W T5 system (4 blue+, 1 coral+, 1 Purple+). I may swap out the purple plus for an actinic, but we'll see. I haven't heard anyone give a strong opinion either way on it.
I've been battling algae problems, so I sent in an ICP to ATI, and shockingly came back at 89% (few times got an 89 on the first test in school, so I was happy). I was low in Iodine, Vanadium and Manganese, all 3 elements dosed in part 3, and I haven't been dosing part 3, so that kind of explains that. I got the supplements and added them as per ATI instructions. I've also done 1 30gallon water change, and will do another 30 gallon change in hopes to drop nitrates down some (11.38ppm per ATI), and with the phosphate levels (0.06 per Hanna) kick start my Algae scrubber into action.
Long story short, a buddy of mine has an SPS tank, similar to yours, but only 75 gallon. It's why I got into the hobby, and once I get this algae issue under control, plan is no more water changes, except maybe 10% a month, and get this thing full of SPS corals.
Love the tank!