Nitrates: API undetectable (target under 10)
Phosphates: Hanna Egg 0.08 (target under 1.0)
Calcium: API 420 (target 400-460)
Mg: Salifert 1320 (target 1260-1380)
Alk: API 11dkh (target 9-12)
pH: ReefKeeper Probe 8.01 (target 7.9-8.3)
Salinity: Veegee Refractometer 35ppt (35ppt)
I use API for any tank that is having N>10, under 10 it's not very reliable but IMO <10 is not an issue. I use Salifert N for tank that have rock bottom N and look through the side of the vial (10x multiplier technique) and usually, it looks pale yellow to clear, usually no hint of pink at all
I don't care for API's calcium kit myself. Used it a few times then when back to Salifert. Much more accurate IMO but at long as you're in a 50 pt range you're golden anyways.
Alk, API is not very good here either IMO, Salifert is better, but I really like the Hanna Checker for this. Very accurate, easy, fast.
I use a Milwaukee salinity meter and will never go back. I ran into a calibration issue with a refractometer and learned a lot. Generally you're good as long as you calibrate with fluid not RODI, but not always. Also the pro refractometer from Marine Depot is the best one, it only has a 20-40ppt range instead of a brine refractometer which has 0-100 and is not made for seawater (most aren't)
pH is one of those I never measure anymore, but I have a Hanna TDS/EC/pH meter that I picked up cheap and that is another one of those best purchases ever.
But then again you didn't ask for my opinion lol
I have 3 separate circuits which I can draw from (all gfci and tested). I want to make sure my internal DT pump(gyre) and return pump are on different circuits.
I also like to have my heaters and return on their own circuit. Mainly because if a heater blows and happens to trip the gfci it will stop the return pump. Which to me is a good thing so it hopefully reduces the chance of nuking the main tank with what ever it spews into the sump.
I also like to have my lights on different circuits so that way if one goes out the other set of lights is still providing some light to anything that wants light.
Nice to have things on separate breakers. You can also wire GFCIs all together on the same circuit as long as they are not daisy-chained, and they will trip out independently. i.e. wire them in parallel not series. If you have your first receptacle GFCI and then wire from the other side to the downstream receptacles, the GFCI protects the whole string. You you don't always want that, so if you wire up the next receptacle from the same side (feed side) then it's not covered by the GFCI.
The age old battle with circuit protection is one that is tricky. You don't want a return pump to trip out your system but you also want to avoid getting dead. The latter is generally more important. But if you GFCI your pump, make sure it's a good quality 20A one (on a 20A circuit) that is rated for pump duty. They make these for sump pumps, so that the starting inrush/etc doesn't cause a nuisance trip. The GFCI trips because something is wrong. If there is nothing wrong and it trips, you're using the wrong GFCI for the job. That's why the NEC recently made it a requirement for sump pumps to be GFCI protected, no matter what.
Light on a separate circuit is always good also, I've had a T5HO ballast pop the GFCI, 13 hours later...fun times