Can't get my FC to stay up

[kentuckybob1952]

I can't get any FC to stay in my pool. I've shocked with cal hypo several times. When I shocked the first time my CC was 4ppm with no FC. Since then after three more shockings my CC is about 1.2 ppm but still can't get FC to stay in pool. I shock in the evening so sunlight should't be a factor. My water readings are as follows PH 7.6 , TA 110 ,CYA 50. Should I keep on shocking in hopes I can get rid of CC and have a FC residule? By the way my pool is clear and by just looking you would't know there was a problem. Thanks in advance for anyone's help...... Kentuckybob

[kentuckybob1952]

I forgot to say that I have a 18000 gallon IG with a cartage filter and vinyl liner.........Thanks Kentuckybob

[Buggsw]

You aren't shocking high enough or long enough, though, good job applying shock in the evening.

Stop using Cal Hypo unless you need to increase your Calcium Hardness.
What is your CH, by the way?

Bring your pH down closer to 7.2 Use about 4 cups of Muriatic acid and drizzle it around the pool. I do 2 cups, circulate water for 4 hours and then retest and then another 2 cups if you need to lower more.

Use liquid chlorine to shock to 15ppm. You'll need a little over 2 gallons of 12.5% liquid chlorine or 4.5 gallons of Ultra or Super laundry bleach.
A little more if you use regular strength laundry bleach. Keep it high until your CC's are gone.

Run your pump 24/7 until this is corrected.