Not sure why you hate chlorine. As for the rash, as someone says, most likely a result of chloramines. The free chlorine (FC) in your pool kills algae, etc. If your FC bonds with nitrogen or ammonia, then you have combined chloramines (CC) which does not have sanitizing power anymore. A perfect pool has a FC in the proper level (lots of factors, lets just say 5ppm but know that you need to look up in a table for your specific situation) and have a CC of 0.
Chloramines, or combined chlorine smell bad, they are eye and skin irritants, and they get in the way of free chlorine trying to do its job. When a pool smells strongly of Chlorine, what smells is not free available chlorine, but chloramines. The ironic solution to the problem of a strong chlorine smell is to add more chlorine to the pool, much more, to break apart the molecular bond of the chloramine. Shocking the pool to remove chloramines also has the side benefit of oxidizing every other pathogenic contaminants in the water, disinfecting and essentially sterilizing the pool water.
Most often CC is created when FC attacks sweat, urine, body oil, sunscreen, algae, etc.
So the more likely solution to the rash is CC, not FC.
As for reusing your backwash, you can do that with a chlorine pool with a tiny bit of work/planning. If you get a rain barrell, take your backwash and simply fill the rain barrel with it. You can either wait for nature/time. etc to break your FC down to zero so as not to harm your plants, or you can buy a product to add that will eliminate any FC. You can also buy an RV water filter and add that to the hose, as the carbon filter will absorb the chlorine. I guess this does not apply to a salt water pool, as you dont want to put the salt onto your plants.
