I've used Triton's ICP test before. The kit is about $49 via BRS. Takes about 2 weeks, but it's well worth it when you consider the overall investment you have in that tank.
Once my SPS dominant 200 gallon is fully up and running, I plan on doing the test at least 4x per year.
https://www.bulkreefsupply.com/icp-o...it-triton.html