I'm adding dichlor but my CYA is not increasing?

[plucky71]

Hello all. Here is my question/situation. I'm adding dichlor but my CYA does not seem to be going up as it should be. I opened my Michigan pool to dark dirty water. So I'm in the process of shocking it. I was assuming my CYA to be low or zero after the winter. I did not test it because the water was so dirty and dark. So I started to shock it using dichlor and liquid chlorine hoping to raise the CYA without adding/purchasing cyanuric acid. After nine 16oz. bags of dichlor my cya is still less than 20. I added five of the nine bags two days ago, and the other four bags yesterday a.m. Filtering 24/7. Water is clean, not sparkling. Still shocking.

ph 7.8
t/a 60
ch 150
cya <20
FC aiming for 12

Shouldn't my cya levels be going higher than <20? Thanks for the help.

 

[JasonLion]

That depends on how much dichlor you have used. The CYA level will have gone up, but it might not have gone up enough to register on the test.

If you know how much dichlor you used, you can use the Effects of Adding Chemicals section of the Pool Calculator to find out how much CYA it added to the pool.

 

[PaulR]

After nine 16oz. bags of dichlor my cya is still less than 20.

Pool Calc says 9 lb dichlor in 12000 gallons should bring CYA up by around 45. What's your water temp? The CYA test reaction goes slower in cold water; the sample wants to be up to room temp so the test will work in a reasonable amount of time.
--paulr

 

[Ohm_Boy]

It can take a couple/few days for the CYA to register.

 

[chem geek]

Dichlor should register the CYA almost immediately, limited by circulation. It is very fast dissolving. If you find that your chlorine demand is very high and that you have trouble holding an FC level, then you could have had bacterial conversion of CYA to ammonia and that might have continued somewhat when you added Dichlor. I hope that's not the case, however, since that may take a lot of chlorine to rectify.

 

[plucky71]

I'll try testing again with the sample at room temp. Thank you all for the input. I'll post back after I test.

 

[plucky71]

CYA is still not going up? I added 32oz. more of dichlor two days ago. That is 171 oz. total, and the CYA is still <20. Could it be bad dichlor? I just purchased the box a week ago at Costco. Could my R-0013 be bad? I bought it last year and stored it in my laundry room cupboard year round. According to Pool calc my CYA should be at 50.
Any thoughts?

 

[chem geek]

Check the ingredients to be sure what you are adding is Dichlor and not Cal-Hypo or lithium hypochlorite -- it should say "99% Sodium dichloroisocyanurate" or "99% Sodium dichloro-s-triazinetrione". If it's Dichlor, then make sure you are using the correct CYA reagent and if you are then maybe it is bad. You can also do a bucket test adding some Dichlor to a bucket and then seeing that the FC is extremely high (OTO test should be at least orange if not dark red) and the CYA test should make the water sample very cloudy. If you have any pure CYA around, you can repeat the bucket test with that. Finally, you can get a CYA standard, though I'd just get fresh reagent since that's more likely the problem.

 

[plucky71]

I just checked the label. It says Active Ingredient- Sodium dichloro-s-triazinetrione........15%. Other ingredients 85%. Available chlorine 9.53%. Is this not dichlor? Is this the reason it is still so low? Thanks

 

[JasonLion]

That is indeed dichlor, but at about one eight of the normal concentration. That explains what has been happening, you didn't add nearly as much dichlor as we thought.

 

[plucky71]

Thanks for the help!

 

[RobbieH]

I wonder what those "other ingredients" are!

 

[plucky71]

Now a year later, I'm hoping to purchase the correct product. Is this the right thing- https://www.backyardpoolsuperstore.com/Stabilized-Chlorine-Granules-56-25lb_p_5345.html

Here is what the product description says-ACTIVE INGREDIENT:
Sodium Dichloro-s-triazinetrione Dihydrate. 99%
OTHER INGREDIENTS 1%
Available Chlorine 55%
Total 100%
EPA Approved

 

[linen]

Yep, that is the stuff you want. Remember to go easy on it. Where is your CYA level this year?

 

[Beez]

Yep, that is the stuff you want. Remember to go easy on it. Where is your CYA level this year?

I did the same thing when opening this year. Found dichlor shock on sale at pool store, so bought 4lb in hopes of raising CYA a little while shocking. Must've been low rate stuff because it didn't do squat to my CYA level...

 

[plucky71]

Yep, that is the stuff you want. Remember to go easy on it. Where is your CYA level this year?

Not sure on current level, but last year it was at zero in the spring. I'll test it after I start shocking and it starts to clear up.

 

[linen]

I would probably measure it so in case it is not 0, you can adjust your shocking FC level. It also is nice to have it as history of your pools long term tendencies. Are you using dichlor again this year to shock? As you may know, we recommend having at least 20 ppm of cya in the pool to help maintain the proper fc level during shocking. This usually makes the shocking process most efficient.

 

[plucky71]

Thanks for encouraging me to do it the right way, I will test it prior to adding anything.