I am new to saltwater and I know I have much to learn. Here are some things I have learned.
I have used API and Salifert liquid test kits for PH. If you want an accurate reading, get a PH meter. The API and the Salifert both show the PH in my tank "somewhere" in the range of 8.0 to 8.2. My digital PH meter shows it to be 7.5.
Dead fish anyone??
I have been using a Instant Ocean floating arm hydrometer that has consistently showed my salinity level to be between 1.022 and 1.023. My refractometer shows it to be 1.026.
WOW - more dead fish!!!! So far I have lost $225 worth of fish because I trusted liquid test kits and a hydrometer by a good brand name. My 29 gallon QT tank is cycling. I bought 25 pounds of 'real' live rock for my DT. Not the aquacultured crap that I bought from 'liverockranch.com" I will be adding more of the 'real' rock as finances permit over the next two months.
My three snails are happy. I won't buy another fish for at least 4 more weeks, and then it will spend 4 weeks in QT before going into my tank.
For you newbies, like me, who are thinking about a marine tank, if you don't have a few thousand dollars to startup with, stick with freshwater. This is a very expensive, and frustrating hobby.

I haven't worked with a pH meter in some years, but I recall that calibration was essential--and a pain. What's it like to calibrate yours?

Calibrating my ph meter takes about 5 minutes. The entire process is guided by a readout on the meter itself. Basically, it tells you to put the end of the meter in a 7.01 control solution. So you do that and it calibrates to that and then tells you when it is done and then tells you to use the 4.01 solution. Repeat and then it is done. Fast, easy, and accurate. A 10 year old child could do it. The meter costs almost $100 and the solutions will add about $30, but considering that the best liquid test kits were off by about 1.0 (ph 7.0 when I thought I had ph 8.0) the loss of fish would have paid for the ph meter and saved a lot of heartache.
If you are having ph problems, throw those useless liquid test kits away and buy a meter. And buy a refractometer for your salinity. You will be surprised at how inaccurate that swing arm hydrometer really is. Throw it away too.
And when you get ready to write back and say yours is accurate, I say, if you haven't tested it against a refractometer, you don't know that for sure. And a LSF that uses a hydrometer is no help since those sales clerks are not really trained to use the equipment right. They are trained to tell you that your water is fine so that you will buy fish.
The best place to go is an independent store that is not part of a chain. The chain stores are absolutely the worst place to go for advice, testing, or to buy anything. They are trained to sell you something, period. If they tell you that you need something that they just happen to sell, you know why. They don't know anything.
For instance, when my fish were in distress, the manager at Aquarium World where I bought the fish told me to immediately do a 50% water change. At the time I did not know that changing that much of the tank without letting the water sit for 24 hours would do more harm than good. All my fish died. I will never buy from Aquarium World again. My fish were in distress because the API ph test said I was at ph 8.0 when I was actually at ph 7.0.