Unable to maintain chlorine levels

[waterbear]

I used an over the counter drop tester (OTO). I also had my levels checked at 3 different pool stores. I have a gunite pool
Here is a summary of the latest numbers.

Temp:80
Saturation Index: 0.4
Bogus measurement
TDS: 850
another bogus measurement
CYA: 50
within the recommended range but won't stay there long if you continue to use trichlor!
Tot. Chlorine: 0.4
Free Chlorine: 0.4
As Poolsean said, you have a huge chlorine demand happeining! You need chlorine until the demand is satified and the chlorine is holding. Unstabilized chlorine would be best. Bleach is unstabilized chlorine.
pH: 7.7
Would leave this alone now until the chlorine demand is met.
Tot. Alkalinity: 139
Adj. Total Alk: 124
Tot Hardness: 314
I wouldn't lose any sleep over these numbers.
Since these numbers, I have added pH decreaser to normalize the pH.
Muriatic acid is more effective and less expensive (but not as nice to work with). ..most of us on here use muriatic acid but either one is fine.
I have also added 4 lbs of trichlor yesterday, but the current chlorine level is around zero.
I thought about your idea that high chlorine may be bleaching out the test, but when I check the chlorine levels about 30min after the shock, it tests in the high range as you would expect ( dark yellow) (greater than 5.0 which is the limit on my tester). It is on the following day that the chlorine levels go to near zero. I wonder if I have an algae bloom somewhere in the piping of filter than I cannot see, although the water is clear. Thank you for the help.

Your chlorine demand might be coming from some other source than algae. I am curious what kind of filter you have and what condition the filter medium is in. Also, have you added any chlorine 'enchancers' or sodium bromide algecides to the water? Both of these can create a hugh chlorine demand. Fertializer washing into the pool can create a chlorine demand. Bottom line, it doesn't matter where it comes from...you just need to keep adding unstabilized chlorine, perhaps 3 times a day, to a level of at least 12 ppm until it is met.

I would also suggest that you get a good drop based test kit that uses the FAS-DPD titration test for chlorine (this will allow you to test high free chlorine levels accurately as well as small levels of CC), along with tests for pH, ALK, Calcium Hardness, and CYA. That way you can take control of your water. The Taylor K-2006 is a good choice but a better 'bang for your buck' is the ps234 kit sold by the administrator of this forum on the PoolSolutions website! I have one, as do many of the forum members, and it really is the best kit out there and the best value for the money!