chemical confusion

[jules]

I am so confused.

Yesterday
FC 1.0
CC  .4
Ph  8.0
Alk 80

I added 1 teaspoon Spa Down and 2 ounces Renew

Today
FC 6.5
CC 1.0
Ph 7.4
Alk 70

I don't understand why my free chlorine and combined chlorine went up. I thought I shocked with MPS to eliminate the combined chlorine. My water is clear and smells better, so I am happy about that, but I just don't get it. I have a 250 gallon tub that I have had since the middle of October and I changed the water 12/21. I'm trying to shock on Saturdays. One week with dichlor and the next week with MPS. I kind of overdid the first tub of water, so I'm trying to keep it simple this time.

Any help is greatly appreciated!

Julie

[chem geek]

Depending on the test kit you are using, non-chlorine shock will register as CC.  2 ounces of Renew (which is 33% MPS) in 250 gallons is equivalent in oxidizing power (and in how it registers on chlorine tests) to 9.2 ppm chlorine.  Did you measure the water very soon after you added the Renew?  If so, then it may be registering as FC on your chlorine test.

Eventually, the MPS will drop, but if you want to use chlorine and MPS you might consider getting a better test kit where you can use an MPS interference remover.  The Taylor K-1515-A is a FAS-DPD chlorine test you can use along with the Taylor K-2042 MPS interference remover.  Instead of the 1515, you can get the Taylor K-2006 if you do not already have a good complete test kit.  If you already have this kit, then just get the 2042 interference remover.

[jules]

Thank you!