Triton is by far your best option, but not the cheapest. The US water testers are hit or miss, and use titrations similar to home test kits. Triton uses ICP which is much more accurate.
I second Diesel's note on alkalinity. I measure daily, and I've actually noticed that since I was dosing at night, my alkalinity was shifting significantly during the day (.5-.8 dkH). I've since moved to dosing 24 hours, and my corals are a lot happier. The most my alkalinity varies is .2 dkH from day to day.