3" Black line around pool

[DaveS2]

Hi,

I'm a new fiberglass pool owner with a salt chlorinator. The pool was completed about a month ago and I finally got all the chemistry within the correct parameters. I keep getting a black line around the diameter at the water level. It's like a thin black film. I scrub it off using a scouring pad which is time consuming but effective. The black line will appear again within a few days and get worse every day until I clean it next. There has also been 2- 5" black oval spots that appeared shortly after the pool was completed. They are not slimy and are a few feet underwater on the wall. A scouring pad doesn't fade them at all. One is gone after putting the chlorinater on "Super Chlorinate" for about a week. The other is faded some. The chlorine concentration is reading 8 ppm but the level is probably much higher as the kit I have maxes out at 8 ppm. The high chlorine concentration seems to fade the black spots but doesn't fade the black line. I suspect the black spots may disappear if I kept the chlorine high for about a month but the water with high chlorine levels makes your skin burn and itch for a few days besides any other problems it may cause to the pool chemistry that I'm unaware of.

Does anyone know about the black lines that appear at wherever the water level is? Maybe dirt from the air pollution in the rain?

Thanks for any advice.

[ivyleager]

Dave,

Could you post a full set of values:
Free chlorine
combined chlorine
total chlorine
pH
alkalinity
calcium hardness
cya
pool volume, type of filter, how long filter runs

Also include any other chemicals or additives you or pool company may have put in pool.

I don't have a SWG, but I see others posting that to conserve cell life, it may be best to superchlorinate w/ an alternative, such as bleach. You may wish to look into this.

Sure sounds like a black algae problem. Post numbers please.

CaryB
Go 'Canes!