Vinyl liner Stain/Bleaching or Algae?

[mts37]

So my pool liner had always had two different shades of color on the wall (unsure of liner age or previous repairs). About halfway down it goes from blue to more of a faded blue. On closer inspection it looks like the color change happens at a seam on the wall.

Fast forward to today - I am not sure if I just didn’t notice it before or if it got worse but there is some bad looking bleaching or staining where the floor meets the wall all along the edges of the pool. What’s even weirder is you can see that the stain suddenly stops at the seam along the floor/wall edge.
Is this some kind of algae? It does not scrub off.
If it is staining what could it be?
If it is bleaching why would it only be at very specific locations and stop at the seams?

see pictures for better idea.

Btw the pool water is crystal clear now after opening - showing no CC and maintaining FC at 4-5 ppm, CYA 30ish. Excuse the dirt/leaves in the pictures I didn’t run the robot yet and we just had a big rain storm with a lot of wind..

 

[Texas Splash]

Unless chlorine was continuously poured at that location without circulation allowing the chlorine to settle, it doesn't make sense to me. I'm also wondering about calcium. Can you post a full set of test results anyways?

 

[mts37]

Ran a fresh set of tests this morning.

FC: 5.7
TC: 5.9
pH: 7.4
Alk: 74
Cya: 31

Don’t have a test for calcium right now but at closing last year it was around 150 and I’ve probably added maybe 30 from some calhypo during opening. It’s probably still around 100-150 when factoring in draining over the winter due to rain.

 

[Texas Splash]

Those seem to be good numbers. Nothing that would indicate a chemistry issue. Can you confirm what test kit you use please?

 

[jay jay]

Could possibly be wear on the liner from an automatic vacuum?
I noticed that my old polaris vacuum would follow a pattern when cleaning the pool, rubbing the tires on the same section of liner.
Maybe watch your auto vacuum for a while and see if it rubs on that edge frequently.

 

[mts37]

Those seem to be good numbers. Nothing that would indicate a chemistry issue. Can you confirm what test kit you use please?

So I’ve been using a LaMotte ColorQ Pro 7 for chlorine, alk, CH, and CYA. I have a lab grade pH probe that I use for pH (technically also have the LaMotte for this as well, but my probe is more accurate).

Once I use up my existing supply of reagents I have been meaning to purchase a TF-100 kit.

aside from the chemistry and the accuracy of my testing now, I still feel like my problem is unrelated to any of that. Something seems odd that the liner at the bottom is a slightly different color starting at the seam along the wall that goes all around the pool. Seems odd that the staining/discoloration disappears at the seam in the shallow end.

Based on the condition of the pool during my home purchase I am fairly certain the previous owners did not take much care of the pool In the years leading up to the sale. Maybe they had to replace the top section of the liner and the top half is new and the floor and lower walls are old?
I just can’t remember if the staining at the bottom is the same or getting worse - my gut feel is worse but it seems to have gotten worse just during the time the pool was closed in winter.

 

[mts37]

Could possibly be wear on the liner from an automatic vacuum?
I noticed that my old polaris vacuum would follow a pattern when cleaning the pool, rubbing the tires on the same section of liner.
Maybe watch your auto vacuum for a while and see if it rubs on that edge frequently.

Thats a good point, but I think the discoloration got worse during the time the pool was closed. I surely noticed some discoloration last year during pool season but it just seemed a lot worse once I opened this year and got the water cleared up.

 

[Texas Splash]

Based on the condition of the pool during my home purchase I am fairly certain the previous owners did not take much care of the pool In the years leading up to the sale.

I think that's going to be your biggest question and potential contributor to the color changes.

 

[mts37]

I think that's going to be your biggest question and potential contributor to the color changes.

Ok that’s what I thought.
I think my biggest concern was that this was some weird type of algae and I should avoid swimming until it’s “fixed”. From the discussion so far it seems like you would agree that this is just staining/bleaching and there really is nothing to do.

I’ll monitor to see if it gets worse and then I can understand if there something i am doing wrong