to answer carls ques. no the liner has a pattern on it. and the one side opposite the return flow is pretty faded.

Duraleigh, I use bleachcalc to adjust clorine levels, but I thought I had alge, maybe I did, I don't know, but I prepared the fight the alge and stocked up on bleach. I put in the required amount for shock level, and it held overnight on the first dose. That was the only time I used an eccess amount of bleach.