total and free chlorine

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

total and free chlorine

Postby chem geek » Fri 28 Aug, 2009 10:52

There's more info on the ColorQ here . Note that the chlorine test is based on DPD so will bleach out (and be inaccurate) at higher chlorine levels, starting to have problems above 5 ppm and not being able to properly register 10+ ppm. The pH test will be sensitive to high chlorine levels, but that's true of virtually all test kits. The other tests can be OK -- CH is off more than a drop test, but CH levels are higher anyway so on a percentage basis it's not bad. CYA seems OK.

pup55, I'm not annoyed. I was pointing out inconsistencies to emphasize the importance of having a good test kit. The Defeating Algae link emphasizes the importance of maintaining a high chlorine level during the shocking process. It's more detailed than I would rather type in each post which is why I refer to it.

Richard


pup55

total and free chlorine

Postby pup55 » Sat 29 Aug, 2009 14:18

I undersatand, you must type this stuff all day. I did print out all the information that you gave me an will work on the pool as soon as I can pick up the test kit. I have 2 different test strips right now and sometimes it is so difficult to try and match the colors up.
Thanks for all your help
Steve
pup55

total and free chlorine

Postby pup55 » Sun 06 Sep, 2009 14:00

Guys I continue to work on my pool to get rid of the algae. I thought I was doing well till I looked at the pool and the algae was back. I still need to pick up a good test kit and right now I am using 2 different test strips. I tested it today and this is what i have. I shocked the pool about 2 weeks ago and thought it was good.
TH 100
TC 10
FC 10
PH 6.8/7.2
Alk 100
CYA 30-50
I have tried everthing to get my TH and TC down but no matter what I do they stay the same. I have read most of the information on this site and I dont see anything on TH and TC being so high and what cause's this? Do these numbers being so high tell me something about whats wrong with my pool. Do these numbers being so high mean that the chlorine is not sanitizing my pool?
Denali
Swimming Pool Superstar
Swimming Pool Superstar
Posts: 257
Joined: Tue 29 Apr, 2008 17:14

Total and free chlorine

Postby Denali » Sun 06 Sep, 2009 22:15

pup55 wrote:Guys I continue to work on my pool to get rid of the algae. I thought I was doing well till I looked at the pool and the algae was back. I still need to pick up a good test kit and right now I am using 2 different test strips. I tested it today and this is what i have. I shocked the pool about 2 weeks ago and thought it was good.
TH 100
TC 10
FC 10
PH 6.8/7.2
Alk 100
CYA 30-50
I have tried everthing to get my TH and TC down but no matter what I do they stay the same. I have read most of the information on this site and I dont see anything on TH and TC being so high and what cause's this? Do these numbers being so high tell me something about whats wrong with my pool. Do these numbers being so high mean that the chlorine is not sanitizing my pool?


Hi,

As chemgeek said test strips aren't real accurate. An example is your pH reading. 7.2 would be an OK level whereas 6.8 would be low.

If you have algae starting up you don't want to lower your chlorine level. If anything you'd want to raise it and keep it up until the algae was gone.

As for the TH of 100, if that is hardness you don't need to lower it.

Once you have a good test kit then you can be confident in your numbers and you can get solid advice on what needs doing.
pup55

total and free chlorine

Postby pup55 » Mon 07 Sep, 2009 06:45

I will be getting a test kit but if my TC and FC are both at 10 would that not kill the algae? I see that most of the people on this site have there TC at 3 and FC at 1.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

total and free chlorine

Postby chem geek » Mon 07 Sep, 2009 14:19

If your CYA were 50 ppm, then you'd need the FC to be around 20 ppm to kill the algae quickly enough. However, with test strips saying the CYA is 30-50 ppm, you really don't know the true CYA level and without knowing that then it's hard to know how high the shock level of FC should be. Nevertheless, if you've got 10 ppm FC and the algae didn't turn from green to cloudy-white, then that does imply that the CYA level may be higher than you think or that the chlorine level isn't what you think it is. If there is a lot of algae, then it should have the FC drop during the day quite a lot -- you have to keep adding chlorine to keep the FC up. It's not a one time dose.
pup55

total and free chlorine

Postby pup55 » Mon 07 Sep, 2009 15:31

The pool did not turn cloudy, I only saw a green tint to the bottom and sides of the pool and it took about 2 weeks for this to happen. Just like you have said all along the test kit makes all the difference in the world. One other question for you, I tried to shock the pool last night with bleach instead of granular shock. When I shock it with the bags from the pool store I will see dead algae on the bottom of the pool the next morning. When I did the bleach last night I did not see any dead algae. I brushed the pool before I put in the bleach and could see all the algae coming off the pool liner. I used 3 gallon bottles which had 6% sodium hypochlorite, which I thought I read that 1 gallon does 10,000 gallons. When I use the poolife turbo shock with 78% calcium hypochlorite I use 3 bags which I was told 1 bag does 10,000 gallons. Does this sound right. The reason I am asking all these questions is that I have had the pool for 9 years and have not changed a thing and this year I have had algae growth. The only thing I did do is have a new liner installed early last year. Thanks
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

total and free chlorine

Postby chem geek » Tue 08 Sep, 2009 01:49

3 gallons of 6% bleach in 28,000 gallons would raise the FC by only 6.6 ppm (and I am assuming you literally mean gallons of bleach -- normally they come in 96-ounces (3/4 gallon) containers though sometimes in 1-1/2 gallon containers. 3 bags of 73% Cal-Hypo would raise the FC by 9.3 ppm (so 78% Cal-Hypo would be around 9.9 ppm) and that assumes the bags are 1 pound each (you didn't say how big the bags were). Neither is nearly enough chlorine to shock the pool, but you were using more chlorine with the Cal-Hypo.

If you can get 12.5% or even 10% chlorinating liquid, then that would be less to carry, but no matter what you use you need to hit it hard and to make sure to add it slowly over a return flow with the pump running at the deep end to ensure thorough mixing. The Cal-Hypo can be pre-dissolved in a bucket and for a vinyl liner pool you can lightly brush the side and bottom where you add the chemical just to be safe.

This link shows you what properly shocking with chlorinating liquid or bleach looks like, in this case with a spring opening where the pool was "let go" over the winter. The key is consistent addition of chlorine to keep the FC/CYA ratio high -- usually where the FC is around 40% of the CYA level.
pup55

total and free chlorine

Postby pup55 » Tue 08 Sep, 2009 19:06

Thanks chem I will be closing the pool soon and the information you have giving me will help me open the pool next summer,thanks again for all your help, great forum.
pool plant man

total and free chlorine

Postby pool plant man » Fri 25 Sep, 2009 03:39

Hi everyone, interseting site. This is my first post and while I am more conversant with Commercial pools, I feel that a couple of details have been omitted from this problem. Adding a chlorine donor combined with Stabalizer will see levels of Cyanuric Acid rising and rising. While adding the chemical, chlorine is added and killed but the Cyanuric Acid does not get killed off but keeps escalating to the stage where the C Acid will 'lock in' the chlorine and stop it becoming effective. You must bring down your Cyanuric Acid levels by dilution with mains water, this is the only way to do this. Once these levels are correct you have a chance of chlorinating sufficiently to kill off the Algie. Also your PH would be better kept at around 7.2/7.3.
Phil

Return to “Pool Algae & Green Pool Water”

Who is online at the Pool Help Forum

Users browsing this forum: No registered users and 0 guests