Sodium Hypo - When it is really hot


New member
Apr 25, 2012
St. Louis, Missouri
Hi folks:

With CYA between 60 and 85 PPM intense sun seems to destroy all sodium hypo and calcium-hypo in my pool. It will go from 4 PPM FC and 0.2 PPM CC at 8pm the night before, I'll add 2 PPM 6% sodium-hypo and the next afternoon 0 FC! My sanitizer demand is 1-2 PPM every 24 hours until the outside temperate exceeds 92 degrees. Once the temperature exceeds 92 degrees there is no amount of unprotected chlorine that can survive an entire day time period. It is as-if it is not mixing with the CYA already in the water. Only tri-chlor can maintain a residual. The amazing part is my pool is positioned to only be in direct sunlight a few hours each day.

Is there any known way to keep a residual all day without a combined sanitizer-stabilizer like tri-chlor?

Viking Gulf Shores fiberglass IG (19,000 ga) with painted concrete patio.
A small fortune in Taylor Tech testing equipment.
TA 100
CH 240
pH 7.5
Temp: 82
LSI Index: As close to zero as I can get it.
FC, CC, CYA see above.
TDS about 1,100 at mid-May startup.
Pool store says no copper or iron in water. No stains observed.
Filter: Hayward 72 ft^2 DE
Pump: Hayward 1.5 HP Superpump.
1 skimmer, 3 shallow returns, 1 deep return. 1 slide.
Water is extremely clear, but I know algae is not far away with 0 FC.

Thanks in advance!
St. Louis, Missouri


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
Once the trichlor dissolves, it doesn't form any special bond that the liquid does, you may be having some delay with the trichlor fully dissolving.

You aren't maintaining enough chlorine for your CYA level. At 60ppm CYA, you should keep it at 7 and never let it get below 5ppm. If it's 85 ppm, you should keep it Above 9ppm and never let it get below 7ppm.


Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
Tucson, AZ
:wave: Welcome :wave:

First realize that it is pretty normal for a pool to require between 2-4ppm of FC per day.

Why do you state such a large variation in your CYA? Are you not doing your own testing?

Have you read through Pool School (button at upper right of page) to get a better understanding of you pool?

For example, if your CYA is 60ppm, you should NEVER let FC crop below 5ppm ... if it is 85ppm, you should not let FC drop below 7ppm.

If your FC is disappearing so fast (and based on the fact you admit to letting the FC drop so low), you likely have something living in the pool consuming your FC. This means you need to go through the Shocking Your Pool PROCESS ... please read the link, it is not a one time addition of powder.

Also, I high recommend you switch to using liquid chlorine (bleach). You CYA is already pretty high which will make maintaining a clear pool very difficult.