I don't think I can reassure you any more than I have.

Short of setting up two identical pools side by side one with high chlorine and one without, and putting your son in one for a week and then the other for a week, there's no way to prove that she's wrong. However, there are NO medical records supporting that, that I've ever seen or heard of.

On the other hand, digestive tract performance is well known -- medically speaking -- to be HIGHLY associated with anxiety. And though I'm having to use 'guess strips' here, there seem to be extremely high levels anxiety in, and around, your pool.

The fact is, this is not a problem we can treat chemically. Well, at least, not with pool chemicals.