Hi:
I got a 90 gal tank and it's going to be two years maturing next February 2019, and I don't do water changes neither since I build up. I don't use Rodi water for my ATO, not even at the first filling. I just add Seachem Prime and there it goes. (No issues with algae or nutrient. Just now because my sump light broke on me and the macro algae died. No algae in the rocks just on the back wall, it's doing his job to maintaining nitrates and phosphate in check plus feed my angels, not good looking, but it's temporary, however my Wifie likes the way it looks, it swing side to side with the water flow, just some trimming once a while) I got a setting very similar like yours but, I haven't upgraded the lights from the Current Marine. I don't have tons of corals because I thru some testing softies and they are hanging there but no grow at all. So I'm waiting till new lights, this year coming up. Saying so, my parameters are some like yours. I don't bother to reach numbers because corals can adapt to their environment and thrive like no bundurys. The key is stability. I could suggest, as many over here, is to set your lights to the right spectrum and par, (because you're tank is tall and this high tech lights aren't just plug and play, they need to be tweet to meet your requirements). You will need a par meter, check were you live if is any other reefer that had one, so you don't have to buy one and after use it, it will be in a closet for ever.
About your PH probably you have high concentrations of CO2 in the room were the tank is, from all your family and pets breathing, saturating the air. Try to run an air line from outside your home to feed the protein skimmer with fresh air, that could give you those few numbers your are looking, but right now you are within acceptable range. Also you could improve your water movement (agitation) at the surface of the thank to help with CO2 exchange.
About your nitrates, remember that you got a deep sand bed. It could be a double blade sword if is not manage adequate. (It's better not to disturb, but if you are going to clean it, just do 1/3 at a time, within weeks). If you are aiming for SPS like all of us lowering that nitrate could help, but as I mentioned. "Corals adapt to their environment, if is stable").
I'm no expert but I'm an school reefer, that just came back after many years. Remember to keep stable your water parameters and be patient because nothing in this hobby happens from night to day.
By the way... A RoDi unit is a well investment gadget. Will give you some peace of mind.
Good lock and KEEP ON REEFING