They use to put an additive in the pool water that changed colour, my old local swimming bath use to use a dark green.
(back in the early 80's)
But they stop using it after a few months as :-
A. It was scaring off the regular customers as there was alway a green tint to the water
B. The kids were peeing in it to turn the water green
and it wasn't me

Never liked swimming so never done it, Mum signed a note to excuess me from swimming lessons
