Switching to Chlorine from Bromine in Hot Tub

Yesterday I switched to Chlorine from Bromine in my hot tub. I drained the tub, rinsed it out and refilled it. I adjusted the alkalinity, PH and hardness and then added chlorine. Everything is fine, the water is crystal clear but a yellowish line has developed at the water line and I don't know why. Could it be due to any residual bromine that was in the water still in the pipes. Or could it be due to bromine residue left behind on the acrylic shell of the hot tub. Or... could it be from the Calcium flakes I added to increase the hardness of the water? Thanks, Peter

I don't think bromine causes yellow stains, nor does calcium. Beyond that, I don't know.

If you could post a full set of test results it would be helpful.