Pool Info: Chlorine Odor & Eye Irritation
It is a common misconception that burning eyes and a strong chlorine smell to the water is the result of too much chlorine. Actually, the cause is not enough chlorine! The combined chlorine compound, called a chloramine, is produced when a free chlorine molecule combines with a nitrogen or ammonia molecule. These compounds smell bad, irritate the eyes and skin, and get in the way of free chlorine trying to do its job.
Shocking or super chlorinating the pool is necessary to oxidize, or break apart the peptide bonds and remove the foul smelling chloramines from the pool water. So then, when the eyes burn and the pool smells over chlorinated, the pool doctor's prescription is to raise the chlorine level ten times the normal amount to achieve a "breakpoint chlorination" threshold which will destroy chloramines (aka combined chlorine). This is required in all pools that use chlorine - yes, even salt chlorine pools.
DPD test kits will allow you to test for levels of chloramines – or to be more accurate, they test for Free chlorine and Total chlorine. When Free and Total tests are the same, the level of combined chlorine is close to zero, but when Total chlorine is higher than Free chlorine, the difference is Combined. It is recommended to shock the pool when combined chlorine levels are 0.3 ppm or higher, or when the test sample turns noticeably darker when test reagent #3 is added.
Other causes of eye irritation in a pool can come from low or high pH levels. The eye has a pH of 7.35, which is a good level to shoot for in your pool. Overuse of some algaecides may also cause some eye irritation and just generally swimming for hours in a pool, often with eyes open, will remove the natural lubricants of the eyeball, and cause “burning” eyes as a result.