We've seen no evidence for concern at levels under 100 ppm* . . . unless you have male breeding dogs who frequently drink from the pool. Apparently, if male dogs drink a LOT from pools with borax levels greater than 50 ppm, it may reduce their fertility.

Of course, if you have teen boys in the pool, that might be a *good* thing.

(Just kidding!)

* FYI: Haven't seen evidence for problems at 200ppm, either, but I haven't heard of anyone trying to reach those levels.