Sorry I am at work at don't have the latest precise results...
we use the Taylor test kit.
but the trend has been this...
Hot, hot, hot-high evaporation- adding water every week.
CYA test in 30-40 range (I added some a few months ago)
Ph is 6.5ish- I regularly have to bring it down -well water is high alkalinity
FC is .5 at best!!!
TA is moderate
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we smell chlorine and don't have algae, but it just doesn't measure!!!

We run the pump 8-10 hrs...
Salt concentration is good levels...
I know, I know, without the exact measurements it is difficult to answer...but I thought I'd post.
Our water is pretty crystal clear...just a puzzler why low measure of chlorine...and the salt generator is set to 80%!!!

first off, you have a very low ph, you might want to double check these figures. Ph should be in the range 7.4-7.8. If you are running a swg you need to get your cya up to at least 70. your fc is probably being eaten up by the sunlight with so little CYA. more precise test results would help too. a numerical value for TA, CC and your correct salt levels. A 0.5 fc is extermely low and chances are you are having an invisible or on the verge of an algae bloom. But to tell, we will need more reliable and correct test results.

Are you sure of your PH measurement? 6.5 is very low and not good for your pool or swimmers. It should be around 7.5. perhaps you had a typo?

What model of Taylor kit do you have? are you testing for FC and CC or TC? Perhaps your CYA is not as high as you think and you are loosing most of your salt cells production to sunlight? Or maybe your cell is not outputting normal amount? Does the cell need to be cleaned or has it been cleaned recently?

Your CYA should be up around 70-80 for SWG. And your target FC for a CYA of 40 is 3 with a do not drop below 2 FC to ensure sanitation.

You need to supplement with liquid chlorine if your cell can not keep up until you find the problem.

The increase in CYA to 80 or even 85 in Texas (see your owners manual on SWG) will help the pool hold on to the chlorine the SWG makes.

You could add some bleach to boost that FC up to shock level for your pool based on current CYA of ~45 which would be 18 ppm FC. That would fight off any algae that may be in the pool currently as a precaution just before you boost the CYA to 80. That will give the SWG a nice level to start from, as the stabilizer takes hold in about 24 hours after addition.

The HTH brand stabilizer is fast to dissolve when added to a Knee-hi and hung in front of a return so the water hits it.

Do check your salt level, as that is essential to producing chlorine.

Okay I am using the test kit from TFP~
FC is still .5
Ph 7.8
CYA is 60, so per the pool calculator for 17,100 gls, I am adding about 3 lbs via knee hi in the skimmer return- that has worked well in the past.
Adding bleach
Thanks for your help...

So you have decided not to shock first? A day or two at shock level before you boost the CYA would be best.

The smell is probably CC (combined chlorine) which is an indication you have something in your water. FC (the good stuff) should not smell. What is your CC, better yet post a full set of results:

FC
CC
ph
TA
CH
CYA

If you are fighting something, it may be using up all the Chlorine your SWG is producing. Just because you can't see, does not mean there isn't some organism in your pool.

I agree with anona, if you need to shock, do that before adding CYA. Shocking process link: http://www.troublefreepool.com/pool-school/shocking_your_pool. Also, I would hang the CYA sock in front of the return and not in the skimmer, in case you need to backflush.

If you want proof whether or not you need to shock, why not bring it up close to shock level tonight and do a OCLT? Link: http://www.troublefreepool.com/pool-school/overnight_fc_test