The dual action tabs are trichlor, so they shouldn't be causing the problem. Let me caution you though--the "dual" part comes from the addition of copper, so if you're not careful the copper level will rise and you'll start having problems with staining of the pool, hair, fingernails, etc, and managing a pool with metals in it is a whole different ballgame than managing a pool without. I highly recommend that if you want to continue to use trichlor, that you switch to a brand of tabs that does not contain copper.

As Watermom requested, please post your calcium, TA, and pH readings....could be calcium precipitating out, but knowing what the numbers are would help in diagnosing it. While you're at it, go ahead and post your Cl and CYA too.

Janet