Algae or scraping from pool brush?

[LisaDLu]

Hello - I have a rectangular pool with a sitting ledge that goes all along the width of pool in the shallow end. The last few weeks I've noticed there is a faint red mark that goes along the length of the face of this sitting ledge. My FC hovered between 4 and 5 in August and has been at least a 6 from September on. I did an OCLT with no chlorine loss.

My numbers today are:
PH 7.6
TA 50
FC 6
CC 0
CYA 80
CH 700
Salt 3400
Temp. 78

When I brush along the bottom of the pool the brush does hit the face of this sitting ledge so I'm wondering if this is the brush leaving a mark or if it is an algae. It is in the shallow end near the pool bottom so the circulation is probably not the best. Any ideas on my next steps to figuring it out? Thanks!

- - - Updated - - -

Also - I checked the pool brush and it is clean. The only thing that is hitting the sitting ledge is the black plastic or the bristles themselves.

 

[kimkats]

Have you felt it? Can you feel it? I am thinking like you in that it might be where the edge of the brush is rubbing the bench. I would put the brush in the water and see if it is where the side would rub. I would also see if it is making a gouge in the plaster.

For the future I would look for another brush for that area. I have a round brush that I use for the bottom side of my inground round pool for the same reason........I do not want the edge of the brush causing problems.

Kim

 

[Texas Splash]

Any chance it could something rubbing-off from a toy or swimwear? Might seem like a stretch, but I can't think of what would cause something red in color.