Your total alkalinity is probably a bit on the low side. I don't know why this occurs, but I've seen it happen plenty of times in my own tub and tubs on my show room floor when I use bromine.
Clear water with a tint of green/yellow is almost always the indicator of low TA. Sometimes it doesn't even have to be off by much, but it can happen.
9/10 times this is the case I've seen.