I would say that CYA measurement of 11 is highly questionable, I assume this is from a pool store test? In general the CYA test range with a good drop based test is from about 20-100 over or under that range the results are very questionable (a reading of 10, could be 0 or could be 15, a reading of 150, could be 120 or could be 300)
either way we now have reason to expect it to be fairly low.
I would suggest adding enough CYA to raise your level by 20-25 ppm then retest (better too low than too high) for your size pool that should be 2.5 - 3 pounds (you don't say how deep your pool is so this is based on a gues of 13500 gallons for a 24 ft diameter pool 48 inches deep)
As chance has it I took a wate sample to a pool store to have tested for iron (due to rustly metal shavings getting in my pool last week), as I don't have a test for iron as it is low in my water normally.
Anyway as expected being a typical pool store their results were WAY OFF on some of the other ranges, they showed my CYA at 10 when it is closer to 30, and they showed CH at 80 when it is really 160, etc.
Ike
p.s. the CYA stabilizer is slightly acidic so will cause your pH to go down some
Also you should start shocking with bleach / chlorine as soon as you can, it will be more effective at the lower CYA level, but if you add CYA powder (hang in a sock in front of return jets) it will take a few days to disolve, oh and yes you wil need a good kit like the TF-100 to shock without wasting a lot of bleach and potentially doing harm to your liner
