I have had, and used borax in my house for sometime. Not only to kill bugs but to make that fun but smelly stuff called floam. I have a home made recipe for it and reading the article here about adding borates to a pool and its toxicity reminded me of a conversation me and several other people had about boraxs toxicity!
Borax has a LD50 of about 3g/kg ORAL in rats. This number changes between companies that do the testing. I have seen it as low as 2.6g/kg. I know people react different to chemicals than rats do but most of our research stems from testing on lab rats. Now this number is for undiluted. So a ridiculously large rat of 1kg would have to consume 3 grams of borax to have eaten a lethal dose of it.
Now the average MALE weighs about 86 kg! so that would be 258 grams of borax a human would have to eat to have consumed the LD50 of borax. Thats a hair over a half a pound of borax. Unless you have a filthy mouth I cant see why any one would intentionally eat it.
Did you know that TABLE SALT has a LD50 that is COMPARABLE to that of BORAX? Yup, its just a couple hundred mg away from borax. Once again the numbers fluctuate according to who does the testing. We all know that too much of ANY thing can be bad for us.
So if in my 1500 gallon I have a borate level of 40 ppm. According the the calc that is 46oz (weight) of borax. More than a half a pound. But in 1500 gallons of water that is only a 0.02% solution of borax! I have MORE salt in my pool (about 3300 ppm) than borax. The ocean has more salt than borates (if any) in it.
Now the main debate about borax has been about dogs. I am no vet by any means but I am willing to bet that the concentration of borax in my pool is by far fatal. Animals react differently to different substances. Which is why vets have a hard time treating animals.
Now this is by no means my way of trying to dispel the belief that the borax in pool water will kill a dog. It can! If he drinks the water continuously for days on end throughout the entire summer. Yeah it could. It would be like slowly poisoning them. But they would have to drink A LOT! Basically they would have to ONLY drink the pool water day after day after day. And even then it would probably leave the body well before the levels of borax in their system could get anywhere near toxic levels.
To make my allready long story short. In my OPINION its harmless unless you get their drinking water from the pool! Yes they will drink some as they are in it. So will you. Its just as toxic as salt is! Do you take them to the beach with ya?
Just wanted to make that point as I think its really important that you know all of the facts about the chemicals you put in your pool. Unfortunately this and salt are the only 2 I know about as far as pool chemicals are concerned!