Small brown spots

[salinity]

Hi all - I noticed some small brown spots on the bottom of the pool today - mostly just past the return. They’re pea-sized and very stubborn - I couldn’t brush or scrape them off with my fingernail. I haven’t tried the vitamin C tab test yet (only have powder on hand), but curious if anyone has any thoughts as to what it may be and if I should be concerned? Our inherited liner is old and “lightly” stained all over the sides & bottom, but these little spots are a seemingly new development.

Chemistry is good - SLAMmed for a day+ a week ago and FC levels are stable. Passed overnight test last night, but CC increased to 0.5 from 0 (we did get a bunch of rain). In addition to Cl liquid I’ve added a bit of pH rise (bucket method) Alkalinity rise (bucket method) hardness up (broadcast) and stabilizer (sock) all according to package or pool math calculations.

Current #s:
FC 7.0
CC 0.5
pH 7.5
Alk 70
CH 75
CYA 50

 

[mknauss]

Anyone broadcast fertilizer near the pool recently?

 

[salinity]

Anyone broadcast fertilizer near the pool recently?

Nope - nothing else in or near the pool except a ton of helicopter seed pods from a nearby maple tree.

Seems unlikely, but I wonder if the Hardness up or Alk up could have done it?

 

[mknauss]

Doubtful that the calcium chloride or baking soda would have contaminants in it to cause that.