Greetings and welcome.
If the stain remover worked, I also suspect metals. Are you on well water?
If metal, the stains will have come back if either you failed to use metal sequestrant after the treatment OR if you've allowed your ph to get too high, which can cause metals to fall back out of solution.
Are you using one of the test kits recommended by TFP to test and control your chemistry? (
TFTestkits.net)
If so, and if all of your other parameters are in order, next time you do a stain removal treatment, follow the instructions in the AA (Ascorbc Acid) treatment thread and then actively keep your ph on the lower side, eg 7.2ish. Here's a link:
Ascorbic Treatment to rid Pool of metal stains
Once you've done the vit c test to confirm, if the staining is mild, if *might* also be removed or lightened by adding a Metal sequestrant like Metal Magic.
I asked about the test kit because managing stains etc. (and in general a pool

) requires an accurate method of testing and being able to rule out other suspects by performing an overnight chlorine loss test, etc. doing an ascorbic acid treatment also requires some precision around bringing up the FC slowly and monitoring the ph after treatment.
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Sue, I've noticed that you're new to this pool...One thing you'll find helpful is to read up in pool school and get one of the recommended test kits for regular water balance before messing with stain treatments, etc. The pool store will keep selling you "fixes" but just as what happened to you this time, there was other information that would have empowered you to make the fix WORK longterm

Eg. I see earlier they told you to add calcium to a vinyl pool, etc.
I know its hard to believe there can be such ignorance at a store that's FOR pools, but believe me, through using the TFP way of pool treatment here, I quickly learned that this is actually often the case when I was new to my pool five years ago!
So take your time and get familiar with testing and balancing your water through TFP, and then we'll help you manage stains, etc. Don't rush into another AA treatment until you're comfortable with testing and your water is balanced.
Please also add to your signature if you have a salt water generator (SWG) -- there are different metal sequestrants used in that case designed for SWG.