Thanks. I should make that clearer.
Basically, If you are having no problems and have a vinyl or fiberglass pool, you can get by without.
But having only the HTH can make it difficult to figure out what's wrong, when something does go wrong . . . and pool stores simply can not be trusted. Much pool store testing is inaccurate, and ALL pool store testing is designed to sell more chemicals, often chemicals that will ADD new problems.
Essentially, the K2006 is a device to help you anticipate and avoid problems AND to keep you out of pool stores!
One issue: you MUST keep an eye on CYA levels. That is ESSENTIAL.
Test strip CYA results are EXTREMELY inaccurate; HTH 6-way and K-2006 results aren't super accurate, but are accurate enough to do the job. However, the HTH only includes enough reagent for 3 tests.
. . . but I'll update the testing info on the main page this weekend!
Thanks again!
PoolDoc / Ben