FC measurement confusion

brunoforestier

Bronze Supporter
Apr 19, 2020
50
Denver CO
My indoor pool has low FC. Using taylor FAS-DPD test, I have to put about four heaping scoops of R-0870 into my 25mL sample in order to see any tinge of pink, and not the usual dark pink I'm more accustomed to seeing.

Do I need to keep adding more R-0870 powder until it turns a darker pink in order to get an accurate test?

When I add the R-0003 for CC testing, it turns to the darker pink that I'm used to seeing, but this doesn't help me measure FC appropriately (in my mind, anyways).

Current water otherwise: 7.4 pH, and acceptable CYA/TA/CH levels.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,718
NW Ohio
You're wasting the powder. If you add a scoop and it stays clear then you have zero FC. The only time that's not true is if it flashes pink and goes back to clear, but that would mean insanely high FC and you'd have plenty of other hints of that if it were true.

So you have no chlorine in your water.
 
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JamesW

TFP Expert
Mar 2, 2011
24,192
When I add the R-0003 for CC testing, it turns to the darker pink that I'm used to seeing, but this doesn't help me measure FC appropriately (in my mind, anyways).
This might indicate a problem with high CC or maybe super high FC.
 

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
93
Homer, AK
I also have an indoor pool and it is used commercially as an aquatic Physical Therapy pool. Checking and maintaining FC and PH is very important to me. I use a 15-gallon liquid chlorine setup by Stenner that pumps a set amount of chlorine into the pool every day. I check FC at least twice a day. If it's low, I turn the pump up and so forth. I think that what you really want to know is whether or not the FC has changed from the last time you checked. I use a Lamotte Color Q and also the Taylor DPD-FAS. They consistently give me different results, but when one goes down, the other one does too, so I make the correction. They are always in the same ballpark. Taylor makes a little gizmo that you put on the bottle of powder and gives you exactly the same amount each time. I use it with a 10 ml sample and it turns pink every time. I agree that if yours doesn't, you have zero FC. If your room has windows, then you have to either add CYA or put a coating on the windows to block out ALL ultraviolet sunlight. If you don't, the Chlorine will dissipate in a matter of hours. My pool room has 3 smallish windows that have the coating so I don't use CYA. I have spent months dealing with pool chemicals but I think that now I have got the routine down. My 10,000-gallon pool "eats" a 15-gallon container of 12.5% CL in 3 months. It costs me $72.00 for a refill. The water temperature is also important. I read that for every 10-degree increase of pool temperature, the FC should be increased by 1 ppm. I keep my FC at 2.5-3 ppm. The temperature is 95 degrees. The nice thing about an indoor pool is that it's not affected by weather, rain, temperature shifts, etc. You can get into a routine. Also, I keep my TA around 75-80. Any higher and you'll be fighting PH. I add about 8 oz. of Muriatic Acid (Baume 22) every Monday. That keeps the PH between 7.4-7.6.
 

needsajet

TFP Expert
LifeTime Supporter
Jan 4, 2016
4,811
Sydney, NSW, Australia
Pool Size
44000
Surface
Plaster
Chlorine
Salt Water Generator
Unless you have commercial regs disallowing CYA in an indoor pool, you could add 30 ppm CYA just for the benefit of reducing active chlorine and be a little less harsh on swimsuits. I suspect you would also notice less chloramine smell on skin. That's a high rate of chlorine for an unstabilized pool (2.5 to 3ppm). It's true that people will sweat more in warm water, so yes, the 95 degree water will lose more chlorine due to bather load, but doesn't actually require a higher FC level for sanitation, unless it's falling below your desired minimum between doses.

Back to the OP, you can dilute your sample and re-test to rule out high FC. You can use distilled water to avoid any effect from chlorine in your tap water. I'd try a 3:1 dilution. If still no pink, then more definitely it's just a lack of chlorine. The CC result seems to be indicating this as well.
 

brunoforestier

Bronze Supporter
Apr 19, 2020
50
Denver CO
Back to the OP, you can dilute your sample and re-test to rule out high FC. You can use distilled water to avoid any effect from chlorine in your tap water. I'd try a 3:1 dilution. If still no pink, then more definitely it's just a lack of chlorine. The CC result seems to be indicating this as well.

I'm certain high FC wasn't a problem, I have been neglecting chemical testing for about a month.

I've been slowing adding more 10% bleach into the pool today, and I've been able to re-achieve FC back to around 2.0, which is just short of what I'm aiming for.

Thanks for the help, everyone
 

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
93
Homer, AK
That's a high rate of chlorine for an unstabilized pool (2.5 to 3ppm). It's true that people will sweat more in warm water, so yes, the 95 degree water will lose more chlorine due to bather load, but doesn't actually require a higher FC level for sanitation, unless it's falling below your desired minimum between doses.
Thanks for the advice. I use a Spectralight Commercial UV unit and have absolutely no chlorine smell. Believe me, if there was ANY smell, I would hear about it immediately. Ditto for bleaching out of bathing suits. The PTs used to treat people at the local gym/health club pool and the chlorine stink would knock me over as soon as I opened the outside door. The suits bleached out and hair would stop growing on the PT's legs. That is a saltwater pool and I would bet that the FC was always over 8. Just guessing. But I hear what you are saying. I bought a Hanna ORP/PH portable unit 2 months ago that I use every day. I will try out the FC at a lower level, perhaps 1.5-2. I want to keep the ORP at over 750 and will keep lowering the FC gradually to see if I can keep it that high. I very much appreciate your advice and all the good advice I get from TFP. I have the pool water tested every month and so far I get very low bacteria levels. I raised the FC by 1 after I read that bacteria like warm water. I want the pool to be safe and comfortable, in that order. I recently put in some MERV-13 air filters (used in hospitals, not operating rooms) that are supposed to remove the virus from the air. I ordered them last August and Grainger just delivered them two weeks ago. Very high demand. I have to say that my decisions on FC have been affected by my virus concerns.
 
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