Those darn tests

tadcpht

Well-known member
Jul 17, 2012
95
Forest, VA
So I have opened my pool for the year and regulated my numbers, but I have a few quick questions. First off, do I need to use the DPD-FAS test for every chlorine reading? I have the regular chlorine test, is that sufficient enough for general chlorine guidelines or should I be using DPD powder every single time? If I test every day I can see where that would be an expense. Also the CYA test seems a bit subjective. Depending on where I am sitting and what light I am looking in the CYA test comes out different. I do it at least twice and average. Does anyone think this? Thanks. Oh and is it better to test in the morning and add chemicals in the morning, or test at night and add at night?
 

pwrstrk

TFP Expert
LifeTime Supporter
Aug 17, 2012
4,758
Elverson Pa.
No you don't need to do the DPD-FAS test every time as long as your target FC levels are 5 or less. I don't even test everyday as I know my pools habits for FC. The OTO test will determine that you have chlorine present. It only reads up to 5 ppm. Your FC level is determined by your CYA level.
The CYA test is light sensitive so it needs to be done outside in full sun with your back to the sun to create a shadow. Hold the vial at waist height.
The best time to test and dose FC is in the evening when the sun is off the pool. That way your water has sufficient chlorine for the next day providing nothing is consuming it over night 😎
 

anonapersona

TFP Expert
LifeTime Supporter
Nov 5, 2008
2,598
I use the DPD test every time, but I only test every other day "in-season" less than that off-season. I can't tell anything more than Yes I have some chlorine or No I have almost no chlorine from the other test.

When to test really depends on what I am wearing.... if I have on good clothes, I may get a sample and test but wait and add chems when I am in PJ's or a swim suit. Still hoping for a bleach and acid proof lab coat some day -- with a TFP patch on the front, of course.

I test both pH and FC every other day, then TA probably once a week, and CYA once a month or so. And when I start a new data recording sheet I test everything, for the record.
 

tadcpht

Well-known member
Jul 17, 2012
95
Forest, VA
Jeff,
Thanks for the info. My CYA is between 50-55 which makes my minimum 4-5 and my target 6-7. Being that my Taylor K-2005 has the drop dpd test that only goes to 5, I should probably use the dpd powder test for my FC tests for now until the splash out rids my pool of some CYA and the target drops below 5. Does this sound right? I also saw on the dpd drop test where you can dilute it to measure higher.....I take it this is not accurate?
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
DPD tests up to about 10 without too many problems. You lose some precision, but for day to day use, with another option available when you need it, it is acceptable. Trying to measure above 10 DPD is useless.

I use the OTO test day to day, just to check to see if something is way off from what I expect it to be. And then use FAS-DPD to check in more detail about once a week.
 

pwrstrk

TFP Expert
LifeTime Supporter
Aug 17, 2012
4,758
Elverson Pa.
First how much sun is on your pool during the day ? You don't want your CYA too low. When you test for FC write down the results and how much you add to reach your target. You'll start to see a trend and you can skip some tests and just dose what your pool needs. Your pool will lose about the same amount everyday give or take 1 ppm.
. 😎
 

tadcpht

Well-known member
Jul 17, 2012
95
Forest, VA
Thanks guys for the replies. When the sun clears my house the pool gets sun all day. I would say from 9-10am until sundown. So I should be able to use the dpd for day to day and just use the powder approximately once a week?
 

pwrstrk

TFP Expert
LifeTime Supporter
Aug 17, 2012
4,758
Elverson Pa.
Yes. I got the OTO confused with the DPD. Sorry about that.
With that much sun on your pool I wouldn't let the CYA level drop below 40.