If the pool is 52" high, the water is probably only 48" or even 46". You measure the height (depth) of the water, not the wall to figure capacity.

Stabilizer can take up to a week to give you an accurate reading. If your CYA=0, your FC=6, and (i'm guessing) your CC=0, why do you want to raise FC any higher?

One thing you CAN consider doing is using pure Tri-chlor tablets (only 99%, nothing lower). Trichlor adds 6ppm of CYA for every 10 ppm of FC, and is very acidic so it can bring your pH down, too. You just have to watch all 3 things.

Now you mentioned salt. If you are using an SWCG with salt in the water you need to keep your CYA between 60 and 80 ppm, and your FC should be at least 5% of your CYA level. So if CYA=60, your FC should always be 3 or higher. If CYA is 80, then FC should be 4.

Are your sure your salt level is at or near the recommended 3000ppm level?