nasty stain on bottom at opening

and panic sets in again... this is my fifth year opening this particular pool, and i've never seen anything quite like this. inground pool, solid cover. i opened today to very clear water, the usual amount of debris in the bottom. (when, oh when, will the worms in my area learn that THEY CAN'T SWIM?) but i digress.

in the shallow end, i had what i thought was a pile of worms, but turned out to be a nasty brownish stain that won't come up with vigorous brushing. it's about the size of a smallish cat, solid, but has sort of a half-circle pattern of curls near the edges.

i think i may be opening about a week later than usual... we had a week solid of rain in the area - so maybe it's far enough along in the season for algae to have taken hold? again, the water looks terrific, all things considered. water temp is about 59 degrees, so i guess the algae theory might hold water (yuck yuck yuck), but if so, i'm wondering why the water would be so clear.

worst case, of course, is that my beautiful two year old liner has a disgusting permanent stain on it.... there definitely wasn't anything there in the fall when i closed. whaddya think?

thanks.

You can try rubbing vitamin C on it, or fill a sock with ph minus and rub the stain. If the stain comes off, it is a metal stain. If it doesn't it may be just staining from leaves, or acorns, or algae. If it is the latter, it will come off with the chlorine in the water. You can try rubbing a chlorine puck on it. If the stain doesn't come off with the chlorine, it may be algae under the liner.

I had some pretty bad brown stains on my liner when I opened my pool this year (from leaves and other organic matter).....After shocking my pool twice and brushing it a little bit, there gone.......

thanks folks. you are correct. what a complete waste of panic! after a good shocking last night, the stain is pretty much gone this morning.