yellowish stains in bottom of my pool

[chuckdog]

Hi all.
My pool has been open for the season about 6 weeks now and the water is crystal clear. I am using the BBB method for the first time this season and I have a Taylor K2006 test kit. I use 12.5% bleach/"shock" to chlorinate and I religiously use the pool pal app on my phone to enter my test results, monitor my csi and lsi, and too see what to add...if anything other than bleach. My levels have been pretty consistent for the last 3-4 weeks. Todays results are:

fc 4
cc 0
ph 7.8
alk 90
ch 225
cya 40

water temp 78

I want to point out that I am not sure if the floor on my pool is painted plaster or painted cement. The walls are fiberglass. I'm not really sure it matters for my problem:

Over the last 2-3 weeks I have begun to notice yellowish stains in a couple areas of the pool. The total area of the stains is around 4 feet x 4 feet in total. From the surface it looks like it could be algae, but it does not diminish when I brush...so I'm certain its not algae. I have not done the vitamin c test or the puck test.

Any ideas or thoughts as to what it could be and/or how to treat?
does it matter that I don't know if the floor is plaster or cement?

thanks!
Chuck

 

[chuckdog]

the bottom picture..the dark blue is the fiberglass wall and the darker rounded image on the left is the reflection of trees in the background. Its an overcast day here in new England..

 

[duraleigh]

I think the salient issue with your pool surface is that it is painted. Stains on vinyl or masonry pools are pretty predictable and somewhat manageable.

I would not know where to begin with a stains on a painted surface...my assumption, but I don't know this, is that the paint can take on stains which are simply not removable.

 

[Swampwoman]

I wonder if it would improve if you kept your PH closer to 7.2-ish -- if there were any chance it were iron, that might help. When my PH gets much over 7.5 I can expect enhanced yellowing from the iron - but I'm on a well and I know it So a vitamin c test should def be in order.

 

[chuckdog]

isn't it recommended to keep the ph between 7.5-7.8? PH of 7.2, as you suggested, seems a little low, no?

 

[Swampwoman]

Not if you have metal content in well water. 7.2 is fine.

 

[chuckdog]

I don't have well water.