I feel that Certified Labs makes the best water treatment available on the market. It's more cost up front but much cheaper in the long run.
Starting with a good source of clean water is great. I've had people collect water from steams and rain water you name it. If you have good municipal water, use it. As far as the folks collecting the water, organics in the water settle out and over time can create a film on the bottom of the stove, that keeps the treatment from being able to protect the metal.
So here is my thoughts:
Certified labs treatment
Test it annually, and not with darn pool kits!!!! Have a lab or someone who has bought the proper equipment to do it. 98% of dealers do not have a lab quality kit, I've got Over $500 in mine
Once a season, in the spring, drain a 5 gallon bucket full, look at it, look for discoloration, sediments, then take a magnet on a stick and swirl it around in the bucket, pull it out, if there appears to be strings hanging on it, further steps are needed...
If all looks well, I'd drain my tank and start over every 3-5 years, just in case there was sediments I wasn't seeing or something, playing it safe I guess