Asking about chemical interactions is being a smart newbie: but, borax is one of the few (only?) pool chemicals that has no bad interactions that I know about. (Chlorine reacts with a LOT of things, which is one of the reasons we try to keep everything else OUT, that doesn't have to be IN. Keeping it simple, minimizes interactions.)

The only thing that's been confirmed is that, if you have high-ish levels of borates (50+ ppm) and your dog drinks a LOT of pool water every day (2+? liters for a 50# dog), by the end of the summer his -- the dog's -- testicles might have shrunk. (There are dog breeders for whom this is a concern.)

For everybody else, I'm not aware of any negative side effects.

Regarding "les-iron", I have no idea what that is, so I can't comment.