Ha Ha. Very funny drew.
But I actually did that.. sort of. The room is still under construction so all the lighting isn't in yet. We tried checking it at night & couldn't see so I put the spa light on. It sure was greener! And the other colors didn't help much either.
Regarding light, the room has lots of glass but I doubt we were in the spa during daylight enough to start an algae colony.
The sanitizer is probably the answer. I was not using it everytime we used the spa; just when the test strip said our MPS was low. From now on I will put in 1 oz after every use.
Thanks to all of you for your help.