I bought a used tub and did not decontaminate at first.
After two weeks I started seeing black streaks (about an inch long) in the seats and on the walls and my water was pretty foamy.
So, I started over. I drained it, scrubbed it down and re-filled it using the bromine for beginners thread. A week later, the black spots were back. I bought a bottle of purge and ran it through, drained it, scrubbed it, filled it, and added bleach to 50 ppm.I let it run for an hour and drain and re-filled it. A week later, black spots. So, I went and got some black algae killer and added it per directions....no change.
A couple days later I dosed it with algaecide again, pretty hard. It foamed up bad and I had alot of scum in the foam. So, I decided to purge it again, scrubbed it down, and refilled it.
That was a week ago. Now, I have more black spots appearing. Algaecide again and it just caused foam that doesnt go away. I dumped it last night and am refilling today with the three step bromine for beginners (again). Can anyone offer any insight? I am at a total loss.