It's not algae, but this seemed like the best place to put the question.
We are still using a pool service the previous home owners used. On their last visit he pointed out what he called "tanning stains". It took me awhile until I realized he meant "tannin". Even with him pointing it out I can't see anything other than the rubber seals where the stairs meet the vinyl liner, and it's still not all that much. He pointed out himself that whatever chemical he would use would be hard on the liner so he doesn't use it often.
I'm sure some of it is personal preference as to when any stain becomes an issue, but for tannin stains is there any reason or need to do anything about it early, as opposed to waiting until it becomes an issue for ME (Or, more likely, my wife)? Being from Northern Wisconsin I'm more than familiar with tannin where many of our lakes, the Wisconsin River, and all reservoirs are as dark as can be from tannin. Our pool is in an enclosure as well so there should be little that could get in there other than maybe leaves on the enclosure and rain bringing it in.
Now that it was mentioned my wife is worried, but I want to leave it alone. So, assuming it's tannin, is there any harm in leaving it until it bothers me or should something be done sooner? Honestly, the areas pointed out are stained only just enough to not be "white" so I'm looking for an excuse to not have more chemicals added to my pool