New here but have been reading up on my problem a bit here and other forums and blogs. This seems like the most knowledgeable so here we go.
I've read quite a bit and it seems most people feel these are either caused by metals in the water or are biological. I haven't had my water tested at the pool store yet but a quick test strip showed FC was low at .5ppm, ph 7.0, TA 100. These appeared almost out of no where.
The pool is about 5 years old and I have never had an issue except for occasional mustard algae which was quickly treated and removed. I have not tried the vitamin c test (water is a bit cold to enter).
Here's my biggest concerned, I have read of 'under the liner molds' that will cause these stains and cannot be removed. Mine are light yellow. From what I've read these under liner molds usually grow in spots that form lines and that's what I have. I have what look like dog footprints starting in my shallow end and traveling almost in a straight line into the deep end...like a dog walked down my pool leaving yellow footprints.
What am I up against here? Thanks to anyone who has advice.