Contrary to popular belief, blonde hair that turns green after swimming is not usually due to chlorinating products. Green hair is usually an indication of copper in the water. Test the water for copper and apply Pool Magnet and Quick Clear according to label instructions.
To remove this green tint from hair, rinse in lemon juice, 1 part vinegar to 4 parts water, or use specialised shampoos available at hairdressing salons and pharmacies.