Sandpaper like stuff on bottom of pool

[motomomof2]

Hello! New to this forum. I have a 24x52 aboveground pool with a vinyl liner. I opened it about a week ago. I am converting to BBB from a frog bac pac system. I have a few questions:
1) I still have bac pacs left. Can I still use the mineral system to use them up? My mineral cartridge was replaced last year, so there are still minerals left in it. I have to use the mineral cartridge to use the bac pacs.
2) There is a sandpaper like feel to the bottom of my pool. Its kinda crusty and is gradually coming up with ALOT of elbow grease. I mean VERY gradually! What can I do to help get this up?

I bought a 6 way tester kit at Walmart. I am getting ready to order the other test kit that you guys recommend.
My readings are :
PH=7.5
CL=6
CH=330
CYA=45
TA=350

[PoolDoc]

Do NOT scrub it -- you will damage your liner.

Sounds like sand algae residue. Take a look: http://www.poolforum.com/pf2/showthread.php?12111-Sand-Algae

It you can confirm that it is sand algae, you need to read this page:
http://www.poolsolutions.com/gd/lowering-swimming-pool-alkalinity-step-by-step.html
and this thread:
http://www.poolforum.com/pf2/showthread.php?16992-Lime-Softening-to-Reduce-Excess-Hardness-Bucket-Test-amp-Treatment-Process

To fix the problem, you'll need:
1. A K2006 kit
2. A calcium bucket test result
3. Use the results of #2 to "lime soften" your pool, THEN
4. Use alkalinity page to lower your TA to less than 60 ppm.

THEN, you'll be able to re-dissolve the calcium deposits on the liner.