It is unlikely that a swimming pool which has not made any of the people who were also using it ill would make your dog ill as long as he wasn’t drinking too much of the water. In most cases dogs take every measure to avoid drinking it since they don’t like the taste.

In any case where drinking too much of the water would make him ill, there would be such symptoms as vomiting and loose feces. This does not rule out the possibility that something unexpected could happen (e.g. a specific reaction to one of the chemicals), but I think it seems more likely that your dog is in fact, very tired!