OCLT

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cood60

cood60

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Jan 20, 2012
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Virginia Beach
I am in the midst of an algae shock
I have 0 cc
I have sparkling clear water
I continue to have an average of 4 ppm OCLT results
So I began to wonder about the 1 ppm or less requirement
1 PPM is 20% of and FC of 5
20% 0f 30 PPM (my Algae shock level) is 6 PPM
So would not 4 PPM be OK?

Just a thought from an impatient shocker
 
At non-shock levels, the overnight chlorine loss is much lower than 1 ppm. In my pool which is kept quite warm at 88ºF an 8-hour overnight loss just over 0.2 ppm (sometimes reads as 0.4 ppm, but usually less). If you had a 2 ppm FC loss overnight then perhaps you could see how things went after you brought down the FC level, but at 4 ppm overnight that truly is quite a lot. The chlorine is reacting with something in your pool, maybe in the filter or behind a light niche or under a ladder. I'm assuming that there truly isn't any significant sun on the pool during the overnight test.

Of course, it's your pool and you can bring down the FC, but if you run into problems you'll at least know that it's because you didn't get rid of the chlorine demand, wherever it's coming from. Personally, I'd keep it up at shock level to see if the loss rate drops.
 
Thanks Chem Geek, I was hoping you would respond!
I jsut did my OCLT reading at 10 PM tonight
I had put enough Bleach to bring it to 32 ppm at 5pm
Checked it at 7:45, it was 29 so I added more bleach
At 10 it was 29,33,29.5 (Did three tests)
I am concerned that the test is not as accurate as I was hoping as I did three separate tests at the 10PM test, thus the 29,33, 29.5.
Seems I am getting a 4 pt swing just in the three tests in a row!
Seems like the FASDPD test can vary depending on how big the drops come out which can vary as squeeze pressure is applied.
Also how important is the amount of 870 powder? Is it better to err on the high side when sccoping it?My lights and ladder have been out for
the entire time. I have a slide, I ran it for the first few days of 30PPM Shock and a few times there after.
Maybe I am just impatient? Have been doing this for 6 days, clear water and 0 CC for the last 3 days
 
Are you using a speed stir, or swirling by hand?

Were your 3 separate tests from the same water sample. IE. You brought a larger than 10ml sample of water into the house and poured out & tested 3 different 10ml samples from that.
Or did you go out and get a fresh sample each time?

As far as I understand it and with my own testing, you need to use a heaping scoop of DPD powder, 2 if you are testing at really high levels. You may fall into the 2 scoop requirement as your FC is so high.
When I'm running at normal FC levels, I use a barely level scoop, say 2 of the largest grains missing from level.
Seems to work fine at low FC, like 3-5ppm. But when you get up there in FC, if you add too little, the water doesn't get hot pink, it's light pink and this yields a false sample. Hot, vibrant, dense pink pigment seems to be the money spot at high FC after you add the powder, before titrating.

So long as you put in the minimum amt, say in your case 2 heaping scoops, than anything beyond that won't effect it at all.
Too little and you will get a low result.
 
I use the speed stir
3 separate tests from same sample
Have not tried 2 spoonfulls
Before reading your post, I did my test this morning, before daybreak, did 2 tests, first one was 4 PPM Loss, the second was 1 PPM Loss
I will try the extra powder method next time
I sent an email to the TFTest kit supplier and hoping he can set me straight as I am sure I am doing something wrong here.
Thanks
Thanks
 
1. The FAS/DPD test is accurate to within .5ppm. The entire purpose of owning this rather expensive test is to obtain that accuracy.

2. If the solution turns pink and stays pink for more than just a second....then you have enough powder. "trying" other methods only introduces other variables into the procedure and confuses you as to how the test works.

3. If you have VERY high FC levels, the pool water MAY "flash" pink and immediately return to clear. If so, add one more scoop.

4. The dropper bottle should be held vertically and drops allowed to fall off the tip. Drop size can matter but is an issue that never comes up if operator uses a reasonable technique.

5. You have organics in your pool and are looking for answers other than organics. Chlorine is consumed by sunlight and organics......that's it and the OCLT eliminates sunlight.

Get rid of the organics first and I think you will find your testing variances will go away.

6. Yes, you are overthinking this test. Keep you FC at shock value until you use less than 1ppm overnight. The FC is being consumed in your pool because you have organics in your pool water.

Sorry if I sound a little abrupt but this test is being successfully performed by thousands of people everyday. It works correctly in their pools and it will work correctly in yours. Test your FC, do so accurately, and then trust your results.
 
Dave, you have been so much help to me, I would never take offence even if you were "abrupt"
I am not questioning the prolonged failed OCLT as much as I am just trying to find out how three different tests, one right after the other, using the same sample can vary by 2-4 PPM. I have been meticulous in rinsing everything 4 to 5 times after and before each test
I do hold the bottle upright
I try to use only enough squeeze to cause the drops to fall ie minimal (with no squeeze pressure, no drops come out)
The water does turn and stay pink/red with a nice heaping spoon
I do use the speed stir, as it is a great time saver....and if I had to "swirl" by hand, I am sure I would lose count on the drops LOL


Please disregard the [/color] etc, I was trying to add emphasis by changing some of the font color and this is what happens, must be some issue with the web site??
 
Try the extra powder...your FC may be just high enough where the test iust not enough powder. The sample should turn a nice bright pink. The only time I have ever had a variance of more than 0.5ppm is when I was being "cheap" with the powder :smile:
 
Finally finished witht he shock. It took 7 days, went an extra day for good measure so really 8 days
Used about 100 gallons of bleach over the process
Pool water was clear and cc was 0 after only 3 days but OCLT showed algae for 4 more days
Am running the pool w/o SWG to let FC come down to normal levels
I think brushing the pool during this is very important, maybe more than the recommended once per day?
I want to thank all of you who were so kind during this process. Love this group!
Cush
 

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Glad to hear it, it feels great when you accomplish something, especially when you beat something into submission. IE. The Algae.

Congrats!!! :goodjob:

So what finally did it for you in eliminating your variances in testing FC?
100gal of bleach? WOOWWIIIEEE!!
Was it a swamp, how many gallons is your pool?

This would be a good time to clean your SWG cell if it hasn't been done in a bit, or at least take it out and inspect it.

I love this forum too, it feels like my home. :mrgreen:
 
No, my pool was never a swamp.(26,000 gallons, see my signature for more detail) It started with yellow stuff gathering in crevices at certain places at the steps. I never could get it all out, even with brushing. It was such a small amount, I just did the best I could with brushing and lived with the tiny yellow patches. It would also gather along the seams and the place where the walls meet the bottom, especially opposite the returns. That yellow stuff would poof away with brushing and not come back for around 4-7 days. I guess I was not sure what the stuff was and it seemed not to wosen for a couple of months.....until the one day I did not check my FC, maybe 2 days, so when I did check it, the FC was 1.5 and the yellow stuff had multiplied. Way more at the usual spots and when I brushed it poofed off the whole bottom (something it had never done before. So that's when I knew I had something to deal with. So, by now, the water was also becoming dull (cloudy), but not green.
When up against my white steps, the stuff was clearly a yellowish light greenish hue. I guess I will pay more attention to any yellow stuff from now on, maybe shock right away when I see it.
 
As I was bringing down the FC from the 30ppm shock level, I discovered that my pool looses very close to 20% FC during the day, with no scource of chlorine. I wonder if this is fairly normal?? I will use rounded #s but here it is:
30x.2=6ppm.(30-6=24ppm) Second day 24ppm x.2=5ppm 24-5=19ppm. 3rd day 19x .2=4 19-4=15, 4th day 15x.2=3 15-3=12ppm, 5th day 12x.2=2.5 12-2.5=9.5, 6th day 9.5x.2=2 9.5-2=7.5ppm, 7th day 7.5 x.2=1.5 7.5-1.5=6 which is close to what my Target FC should be (according to cya chart, wish I could put a link to the chart but I don't know how
Anyway , just a tid bit about chlorine loss
 
Most of the chlorine loss from sunlight comes from the chlorine bound to CYA so the overall loss rate is roughly proportional to the FC level (i.e. falls as a percentage of FC). Technically at high shock levels, there is more active chlorine that gets broken down at a much faster rate so at high shock levels you may find a higher loss rate percentage than at lower levels, though you didn't see that in your case.

As was noted by Jason, this percentage loss rate gets lower as the CYA level in the pool gets higher due to CYA's shielding effect of lower depths.
 
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