Okay, I gotta suspect algae. If you have had the water in your pool since May, and it's been clear till now, then this has to be an algae bloom right? Otherwise if it were metals, you would have been adding maintenance doses of metal sequesterant, I would think, or seen other evidence of metals before now... That being said,
your TH of 500 has me a bit concerned. Your TA is also high and the combination can result in scaling, especially if your PH changes....You need to
order a good test kit and get to the pool store while you wait for your kit, and have them test the water, running a complete set, including metals and find out your CSI - saturation index. If they use strips to test then they are not very accurate either.
In any event, lets proceed on the assumption it's algae. It's going to take ALOT of chlorine.
How deep is your pool? According to the Pool Calculator, An 17 X 36 rectangle, with a depth of 3.5 feet is 17,500 gallons. That's alot of water, and I suspect since it's inground the depth is more than that.
Do you know your exact gallonage or the depth of your pool?
In any event, for 17,500 gal it's going to take about 8-9 (large jugs - 174oz) jugs of bleach to bring you to shock level of 24 (I'm assuming here your CYA is 40-the strips are in accurate) because this could be a type of mustard algae from what you are describing....or your CYA could be higher than what you think so I personally believe that for now, till we know more, a shock of 24 is a good target for you.
So in other words, back to Wal-mart! to stock up. OR if you can get a better price on the 10-12.5% liquid chlorine at a pool store then buy all means stock up on that,
be sure to use The Pool Calculator for proper dosing amounts.
To confirm metals - You can try putting a vitamin C tablet on the brownish areas if there are any on the walls, if it goes away after 30 seconds there are metals present.
So you will have a lot of bleaching and brushing to do over the next several days. Read the article
turning-your-green-swamp-back-into-a-sparking-oasis-t4147.html and it will help explain alot.
Hope this helps and doesn't leave you feeling overwhelmed.