Salifert is pretty much the standard to use. Getting into something with higher accuracy will be a big jump in price (like Salifert is cheap:irked: ).
Hanna now has a photometric readers for phosphate and nitrate (is the nitrate only for FW or can you use it for SW, but I remember reading just a fragment about that, but I'm now drawing a blank). These photometers are very accurate, but expensive, and you need a separate unit for each parameter being tested. I'm not sure why they can't make one piece of hardware with interchangeable reagents. then I might spend the money. But, as far as "standard" liquid test kits, anything "better" than Salifert, such as LaMotte (good for PO4) or Hach, and you're looking at a serious investment.
BTW, I find water test kits for pH not terribly accurate. It's hard to follow you pH though a daily cycle, so a pH probe/monitor is, IMHO, a must, especially with a Ca reactor, and, while I may get yelled at, a Kalk reactor or even a drip. ORP probes are also nice to have, but far from a necessity if you're not injecting ozone. PinPoint now offers probes for Ca, and nitrates, but I've heard (don't you love rumors) that they require frequent calibration to provide accurate results.
Welcome back to chemistry class :banghead:
Henry