Using dichlor to shock

[d.sebens]

Before I realized I could use bleach I bought some “shock”. Turns out it is sodium dichlor. I am using bromine so no need for cya. I already own it but I assume I probably shouldn’t use it due to cya being added for no reason?

[RDspaguy]

We have debated if cya will interfere with the chlorine oxidizing the bromide, but I don't think any conclusions were drawn. Bromine itself is unaffected by cya.

I'd say if you can't return it, use it until cya reaches 30 then switch to liquid. No point in throwing it out.

[d.sebens]

Sounds good. I’ll have to use my test strips, that should be accurate enough to know when to stop. My taylor bromine total test kit doesnt have a cya test included right?

[waterbear]

if your bromine level rises about 10 ppm when you shock then it's not a problem. Bromine is not affected by CYA but there might be some small impact on how effectively the chlorine oxidizes the bromide reserve in the tub. However, as long as the shock brings the bromine level above 10 ppm you are good to go.

[waterbear]

the cya added by dichlor is cumulative at a rate of 9 ppm for every 10 ppm of FC added. so if you want to know how much has been added on a fresh fill you can track the FC level. For example, if you initially add enough dichlor to raise the FC to 10 ppm you have added 9 ppm CYA. The next time you add dichlor your FC is at 2 ppm and you rasie it to 4 ppm so you have added 2 ppm FC with the dichlor. The next time our FC is at 1 ppm and you add dichlor to raise it to 4 ppm which means you've added 3 ppm of FC. next time your FC is at 1 ppm and you shock to raise it to 10 ppm which means you have added 9 ppm FC.  at this point you have added 10 + 2 + 3 + 9 ppm FC or 24 ppm FC. IF you continue to to this until you have added 33 ppm FC you will then have 30 ppm CYA. No need to test CYA.