Chlorine Allergy

[whatwhat]

Hi all. When my little boy was 4 he went into my mother in laws hot tub. He came out in a rash, which over repetitive use became much worse, resulting in his little body swelling, flu like symptoms and a nasty rash. A and e said he would get worse each time he went in, so never to go in again. Which he hasn't. He has always been fine in swimming pools, private or public, without even a hint of anything. He is now 7 and we have just come on our first family holiday to lanzarote. On the first day we took him to a water park, and then home to the pool. That night he looked a bit spotty and a bit pink :-( we put it down to slight sunburn. The next day we kept him out if the sun, but he did pop in and out of the pool. The next day he was covered in rash (although mainly on his face) I took him to the doctors and they have him anti histamine, ibuprofen and steroid cream. We obviously are not letting him back in the pool or back to the water park, although there is a chance that only one of the chlorines has affected him. Sorry for the long post, but we were wondering if there was any way of testing him for different chlorines?? And if we ever come away again, (or even use a different swimming pool) wether there was any way of finding out what Chlorines where used?!?! Thank you very much in advance for any thing that may help him..