HI – brought in our friend Matt from APi who understands the ins and outs of water chemistry to help us with your question. Here is what he shares:

I’m not familiar with the UV system that he is referring to, nor what wavelength it is set to or that it provides. As you know, disinfection and chlorine longevity is mostly determined by pH (hypoclorous acid/hypochlorite ion ratio), and the LSI index. In UV treated pools, UV systems set to the wrong wavelength will not only destroy chloramines but free chlorine as well, this also happens if the flow rate is too high. Proper stabilizer level (25-50ppm) should help, just like in traditional chlorinated pools, but my opinion is that the sales pitch of less chlorine is more myth than reality. It’s true that UV renders certain contaminants inert, thus limiting chlorine demand, but with the factors I listed you can see they also create an environment that makes it harder to carry a chlorine residual, frequently leading to more chlorine usage. UV shouldn’t cause a lower pH, but increased chlorine tablet usage (to carry a residual) could lower pH. Since his pools treats dogs, you should probably recommend the use of a weekly enzyme in your answer to combat the oils that come off of them in pools. I hope this helps!