FC, CC, and TC

noresull

Well-known member
Jul 2, 2012
46
So, I'm looking through the test procedure for the FAS-DPD test and saw that TC is equal to the sum of FC and CC. Does this mean then CC would be equal to subtracting the FC from TC? I ask cause I have better access to free and total chlorine testing more than the FAS-DPD and was just wondering if this is an accurate method for getting CC when needed.
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
Yes, CC = TC - FC, and TC = FC + CC. The tests which measure FC and TC are not as precise or accurate as the FAS-DPD test, but they good enough for daily testing when your FC and TC levels are 5 or lower.
 

noresull

Well-known member
Jul 2, 2012
46
JasonLion said:
Yes, CC = TC - FC, and TC = FC + CC. The tests which measure FC and TC are not as precise or accurate as the FAS-DPD test, but they good enough for daily testing when your FC and TC levels are 5 or lower.
Jason,

I will be using a Hach DR/890 for my testing using the high level chlorine test procedure. I will also be using the same instrument for my CYA readings. Is anyone else using the DR/890 colorimeter for their pool testing that would care to give any tips for them?
 

noresull

Well-known member
Jul 2, 2012
46
I do have a question. Is there any reason why I can't continue to feed dichlor for my chlorine source until I get the CYA up to about 30 or 40 ppm and then begin using bleach? I have been testing it daily with the FC, CC, and pH to make sure I'm not getting it to high.
My current readings tonight:
FC 7.0 ppm
CC 0 ppm
pH 7.1 (dosed with Muriatic Acid a few days ago to lower TA)
TA 252 ppm
CYA 22 ppm
 

anonapersona

TFP Expert
LifeTime Supporter
Nov 5, 2008
2,598
Around here, we typically advise newcomers to dose all chemical separately just because the math can get tricky. If you can handle the math and keep good notes, the other sources of chlorine are fine to use. Just pay attention.

Since you know the total CYA you want to add, you can calculate the volume of dichlor that equals(see Pool Calculator, Effects of Adding Chemicals, at the bottom). Then use that dichlor over a period of days to raise FC. When you have used that volume of dichlor, switch to bleach or liquid chlorine. You should recalculate all your values, probably daily, to be sure that as CYA increases each day, that you are aware of the changing values for min, goal, and max FC (max being mustard shock FC for that CYA). It is a bit of a challenge and only the truly nerdy ought to follow that path, IMO. (Today dichlor raised CYA to 25, so new FC goals are blah, blah, blah, tomorrow CYA will be....)

It is way easier to just put in the CYA you need and be done with it, it is there, you know it is, and you know that eventually it will show up on test, this week or next. Then you can focus on FC, or pH and then FC as the case may be.

That dichor will keep just fine, you will have a chance to use it eventually. Probably next spring, when CYA is just a little low.
 

noresull

Well-known member
Jul 2, 2012
46
Thanks for the tips! I have been constantly adjusting my FC target depending on my CYA reading daily. The pool has looked crystal clear since day one thanks to you guys and the Pool School.

I am a water chemistry nerd and I am having as much fun taking care of the pool as I am using it!

I will be draining the pool completely this fall and storing it then redoing my placement of the pool and planning a major landscape design so the remaining dichlor will be used next spring for sure.

Thanks again for all the help!!