White gritty film on bottom of pool

[Pacificpooler]

We have been trying to get a white gritty type film off of our bottom for about a month now. We have a above ground 24' pool and just got a new liner 3 years ago and have never had trouble with our pool and last year we did not get a chance to cover it. So when we started cleaning we had a mess but after lots of shocking we got it pretty clear now except for all this film on bottom of pool. Some areas it looks dirty a little and when I vacuum everyday it must be moving a bit because it gets cloudy. I have been using First aid for pools and a metal magic and nothing is working.

[PoolDoc]

If it's what I think it is, neither Metal Magic or Pool First Aid are helping a bit. It sounds like sand algae residue; you can check here: http://pool9.net/algae-sand/

Another way to check: get a bit of the scale (1/4 teaspoon), dry it on a paper towel, and put it in a CLEAR wine glass. Add white vinegar. See if it fizzes. If it does, it's calcium deposited by algae.

To fix it, you need to lower your pH and alkalinity.

+ Get a cheap OTO / phenol red test kit at Walmart or Lowes.
+ Get a gallon of 31% full strength muriatic acid at Lowes or Ace -- do not get 'safety' or 'improved' acid!
+ Read this page on handling muriatic acid: http://pool9.net/ma/
+ And this one on lowering alkalinity: http://pool9.net/alk-step/
+ Lower your pH to 7.0, but NO LOWER. Low pH will damage liners. 6.5 is OK, but you can't test for that.
+ Order a K2006, so you can test for calcium and alkalinity. http://pool9.net/tk/

Of course, if it's not sand algae, don't do lower your pH, but do tell us more.