Never had this before. I just noticed a yellow ring around my tub where the water line was, I say was, because the water had been at a higher level and some evaporated. It wipes clean, except for a strip about 2 inches that won't come clean. Also, when I went to clean my filters, they had a yellow residue on them, cleaned up pretty good, but not 100%. Chemicals are good.
We do use soft water to fill and then put in what my dealer recommends to harden it.
What do you experienced tubbers say it could be?
Thank you.