If the pH is 7.0 to 9.5 (or thereabouts), you're OK. If the pH goes to 11 or higher, you must drop the coolant immediately.

Get on a SCA program. You'll need to choose one: The WIX/NAPA/Nalcool/Pencool, and the Fleetguard DCA-4. Either one works. The WIX/NAPA/Pencool stuff is more widely available, in my experience. If you have a bunch of diesel engines, buy a half-gallon of the SCA and a whole jar of test strips. Keep them in a cool, dry area.

You'll need to get the test strips for the additive package you choose - Pencool or Fleetguard.

When you change out the antifreeze, if you have a "complete" antifreeze package, take a test strip for reference.

Every 300 hours of engine run time, take another test strip. Add SCA per the test strip's recommendations. I often add only 70% of the recommended additive, then I'll run the engine for a few hours to get the SCA to circulate, and the next time the engine is cool, I'll pull another strip and see how much more I need to add.

If you add too much SCA, you'll need to drop the coolant again, because too much SCA raises your pH very quickly.