And my eyes stung a little after 4-5 hours of swimming.
And you are surprised???????

That's why goggles were considered one of the BEST advances in competitive swimming--it allows the athletes to train much longer without eye problems.

Combined chloramines are one of several potential sources of eye irritation. High chlorine levels in a clean pool will have little if any effect. Other things can reduce irritation much more, such as:

1) reduce CC to 0.
2) Raise pH to 7.6-7.8 Irritation is lower there as it's closer to human pH.
3) Keep away from all the junk pool stores push you to throw in your pool. A balanced pool is the least irritating.
4) Contaminants. Sun tan lotion, sweat, little kids peeing in the pool all are irritating.
4) Add salt to your water. I don't know the ppm level but if your salinity of your pool matches the salinity of tears, it will be FAR less irritating.

But don't go blaming chlorine for your red, burning eyes!