They are just trying to scare you into a more expensive plan.
But you know what, they are not lying to you about TDS. Adding liquid chlorine (bleach) does raise TDS. But that is not the whole story. That is the story that sounds bad, when actually it is quite benign.
First, it is important to understand what makes up TDS. Most of it is salt, plain old table salt, sodium chloride. The second highest component is usually calcium.
It is also important to understand that any form of chlorine add to the pool has a byproduct it leaves behind. So you must choose which byproduct is the least problem long term to leave behind.
Pucks, dichlor, trichlor, granular chlorine - leaves Cyanuric acid behind. Eventually building up to levels that prevent effective chlorination.
Cal-hypo leaves behind calcium, eventually building up calcium to the point you have scaling.
Liquid chlorine leaves behind salt, sodium chloride.
Really what you need to know is not TDS, but TDS minus salt. In pools with salt water chlorine generators, salt is purposefully added and the TDS is always going to be above 3000. Even if you do not have a salt water chlorine generator, the slow build up of salt from liquid chlorine is going to take a long time to get to this level that is purposefully added for SWG pools.
You won't taste salt until it gets above 3400 ppm. The oceans are 10 times that amount. Use the liquid chlorine and feel confident you are not missing something with the TDS scare from the store.
Phosphates? - keep you pool in balance, and proper chlorine and this is never a problem. The store just happens to have something they can sell you to reduce phosphates.
