Using Calcium Hypochlorite to shock pool

[ErniesPool]

I just used 4# of calcium hypochlorite to shock my pool, as I have developed mustard algae thanks to the rain floods in Texas. I should be reading about 25 ppm of chlorine, but my Taylor test kit shows almost no chlorine! It dropped my pH from 7.8 to 7.2. Why don’t I register chlorine with the test kit?

19,000 gal in-ground plaster pool; plaster older than 10 years

 

[Isaac-1]

Which test kit do you have?

If it is the K-2005 the DPD chlorine test will bleach out at high levels, this is why we do not suggest it, instead the K-2006 has the FAS-DPD chlorine test which will read high level of Chlorine

 

[ErniesPool]

I’m using K2006 with the DPD test, and I have read chlorine levels in the upper 20s before with no problem.

 

[JasonLion]

Chlorine is constantly being lost, to sunlight, to algae, to other contaminates in the pool. So you need to be constantly raising it back up.

If you post a full set of water test results we can give you much more specific advice.

 

[ErniesPool]

Chlorine is constantly being lost, to sunlight, to algae, to other contaminates in the pool. So you need to be constantly raising it back up.

If you post a full set of water test results we can give you much more specific advice.

I will run a full set tomorrow, but I added 4 pounds of 73% sodium hypochlorite at sundown and an hour later I got almost no pink when I used the DPD powder. Something is strange. My issue has nothing to do with sunlight loss. I’ll post a full set of reading tomorrow.

 

[tim5055]

If you have that much chlorine demand it's time to SLAM the pool.

Pool School - SLAM - Shock Level And Maintain

 

[JasonLion]

If you have a full algae bloom or an ammonia problem then losing all of your chlorine is to be expected.

 

[ErniesPool]

If you have a full algae bloom or an ammonia problem then losing all of your chlorine is to be expected.

OK. Here is what I did. I did have mustard algae on the sides of the pool but the water was clear ... no green algae visible in the water. I was coming out of the winter with the pool and had periodically added chlorine bleach to keep some chlorine in the pool until I was ready to balance it for swimming. So, since my cyanuric acid was almost zero, I decided to use some pucks from the pool store. While there I picked up some packs of calcium hypochlorite to shock the pool (normally I shock with liquid bleach) and a bottle of diammonium sulfate that is supposed to kill yellow algae. I followed the instructions and sprinkled the algae stuff around the perimeter, followed by 4# + 1 gallon of 8% bleach.

An hour after running the pool I was amazed to see no chlorine present in the pool. It ran all night and here are this morning’s numbers:

chlorine - 0
pH - 7.4
Total alkalinity - 40
calcium hardness - 300
cyanuric acide - about 50-55

I’m thinking of now going back to the bleach shock treatment, and add enough bleach to bring the pool to 22 ppm chlorine.

 

[tim5055]

Read the directions on SLAMing your pool in the How To section of Pool School and follow that procedure completely to the end. No more magic potions form the pool store.

• CC is 0.5 or lower;
  
• You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less);
  
• And the water is clear.

When all three are true, then follow the additional directions for Mustard Algae.

 

[Saturn94]

It looks like the stuff you added to kill the mustard algae may have added ammonia to your pool, which will eat up CL big time.

 

[Patrick_B]

I don't know, but I would think the Sulfate could act as a Chlorine Scavenger. Does your kit have the FAS/DPD FC/CC test? If so what was your CC level?

 

[ErniesPool]

I don't know, but I would think the Sulfate could act as a Chlorine Scavenger. Does your kit have the FAS/DPD FC/CC test? If so what was your CC level?

Almost none. 0.5 CC.

 

[zea3]

Diammonium sulfate, sold as Yellow Out, creates an extreme chlorine demand. Read more about it here .

 

[duraleigh]

Pool_dufus

TFPC tenant - Never put chemistry in your pool when you do not know the outcome

TFPC Tenant - Pool Stores can and will sell you most anything....whether it helps or hurts your pool.....they just don't know any better

Logic would then encourage us to stay out of pool stores if we want to manage our water via TFPC.

That may come across as being kind of a you-know-what, but it is factual and advice we teach every day. We must not be emphasizing it enough.

 

[jblizzle]

The CYA dropping to zero points to an ammonia conversion ... Which equates to high FC demand.

Plus sounds like the products you added also result in a high FC demand.

Time to start SLAMing with bleach, and lots of it to remove the chlorine demand.

 

[ErniesPool]

The CYA dropping to zero points to an ammonia conversion ... Which equates to high FC demand.

Plus sounds like the products you added also result in a high FC demand.

Time to start SLAMing with bleach, and lots of it to remove the chlorine demand.

Yes, it was the Yellow Out compound that caused my problems. I have now added bleach and gotten my CL level back up into the 20s. With the constant tropical downpours we are having its going to be difficult to hold the shock level up, but I already can see come effects on the yellow algae. Thanks to everyone for their comments. I have learned my lesson. Stay out of the pool store!!