Question about TF-100

[rio]

I have a TF-100 kit that I bought last summer. So it is one year old, but has been indoors at all times (always kept at room temperature).

When testing for FC, I fill the cylinder with 10 mL of pool water and add a heaping spoon of DPD powder, as indicated. The water turns pink and I start adding drops of R-0871 and count until it turns clear again. However, after the water turns clear, about 10-15 seconds later it starts to turn pink again. So I add 1-2 more drops until water is clear again. 10-15 seconds, water starts turning pink again, and so on. I guess my question is: should I keep going until it NEVER turns back to pink again? Or should I stop whenever the water turns to clear the first time? (regardless of whether it eventually turns back to pink on its own).

I use the "SpeedStir" gadget to keep the water swirling continuously.

To give a more concrete example, with my most recent test: the water first turned clear after about 8 drops (4 ppm). It wasn't until about 24 drops (12 ppm) when the water stayed permanently clear. I took the same water to the pool store for a reference and they tested 10 ppm. I have been targeting 10 ppm with liquid chlorine as I just opened the pool with lots of visible algae and very low CYA. So 10-12 ppm is what I'm actually hoping for, but I want to be sure.

I don't remember noticing this last year when doing FC testing. So I'm wondering if the DPD powder or the R-0871 solution have expired, or if last year I was just a lot more (or a lot less) patient.

 

[Richard320]

The first time it goes clear is the result. My sample always turn pink again while waiting for me to finish the other tests. (I have multiple stirbars so I can do all my tests before I have to do the dishes)

 

[rio]

Thanks for the response. I'm still somewhat confused because now I've gotten my water tested at 2 different places (each of which has a different testing method) and they're both giving 10ppm for FC and 10 for TC (so 0 CC). Whereas I get like 2ppm FC and 8ppm CC using my DPD-FAS kit (TC does add up to the same). Is there a chance my DPD powder has lost its effectiveness after sitting around for a year? The water looks really good good, too. I opened the pool 2 days ago and it had lots of green algae, but after lots of scrubbing, backwashing and chlorinating it's crystal clear now.

 

[Richard320]

Thanks for the response. I'm still somewhat confused because now I've gotten my water tested at 2 different places (each of which has a different testing method) and they're both giving 10ppm for FC and 10 for TC (so 0 CC). Whereas I get like 2ppm FC and 8ppm CC using my DPD-FAS kit (TC does add up to the same). Is there a chance my DPD powder has lost its effectiveness after sitting around for a year? The water looks really good good, too. I opened the pool 2 days ago and it had lots of green algae, but after lots of scrubbing, backwashing and chlorinating it's crystal clear now.

I suppose it's possible. When you add powder and mix it up, do you have a few extra granules left over? You should. That's how you know you have enough powder.

I'd still trust your results over a store's test.

 

[rio]

Hi Richard,

Actually, I don't have any granules leftover. And, now that you mention it, I do remember having them last year. Should I try using more powder?
If my results are correct (low FC and high CC), then I would need to SLAM to get rid of CC, correct? But, I don't want add all that chlorine to the water if I don't have to. That's my dilemma.

 

[Richard320]

Hi Richard,

Actually, I don't have any granules leftover. And, now that you mention it, I do remember having them last year. Should I try using more powder?
If my results are correct (low FC and high CC), then I would need to SLAM to get rid of CC, correct? But, I don't want add all that chlorine to the water if I don't have to. That's my dilemma.

Yes, repeat the test and make sure you have a few grains of undissolved powder before you start with the drops.

If you have really high CC, it could be ammonia, or antifreeze, or interference from MPS shock.

Bleach is an oxidizer - it burns things chemically. Sort of flameless combustion. Fire oxidizes things, too. If you have a really hot fire, you don't get much smoke. If you do get a bunch of smoke, what do you do? Fan it. More oxygen. Get it burning hotter. Same thing in the pool. CC is like smoke, imcompletely burnt stuff. You want to eliminate it? More oxygen.

 

[rio]

Thanks again. I'll give it another shot with more powder.

Ammonia would make sense since my CYA level plummeted between when I closed it last year (>100) to when I opened it this year (<20). I've now raised it to about 35.

 

[borjis]

Keep in mind cya consumed by bacteria doesn't always result in ammonia. The process does often enough convert it to nitrogen I remember reading here in posts.

If you had ammonia you would not be holding any FC 15 minutes after dosing. The 2 cannot co-exist together.

 

[rio]

Thanks borjis, that is useful info. I am holding at least 2 ppm of FC so that's good to know. I did just try adding more powder to ensure not all of it dissolves and it gave me the same results. So at this point I am inclined to believe my own test results over the pool store's which means I have a CC problem to take care of.

 

[rio]

Ok, I'm starting to get more confused here. After testing FC at 2 ppm, I added 2 gallons of 12.5% sodium hypo (this should increase the chlorine in my 25k gallon pool by 10 ppm). 30 minutes later, it still tested 2 ppm. So I added 2 more gallons. One hour later, it tested at 1 ppm. That's 4 gallons (potentially 20 ppm) in less than 2 hours. That's 10 gallons since I opened the pool 2 days ago. Should I just keep going? The pool looks great, water is crystal clear, and the CYA level is around 35.

To add to the original question in this post: I've noticed that if I let the water sit for a little after adding the powder, BEFORE adding the drops of R-0871... say, 1 or 2 minutes, the water turns even darker pink, and then it will take many more droplets of R-0871 before turning clear. In other words, my measurement of FC is dependent on whether I choose to wait a minute between adding the powder and adding the droplets. What does this mean? Is there something about my water that makes it take longer to "process" these reagents? Similarly, using the daily blue-box method, when I fill it with pool water and add 5 droplets of the yellow stuff, at first the water is light yellow (1-2 ppm). But after sitting for a few minutes it gets much darker. So this goes back to my original question: which should be the more accurate reading, the immediate one, or the one after letting things settle?

 

[borjis]

What I do is, fill to the 10 ML mark with a pool water sample from the deep end (make sure you get the sample from the same deep end area every time)
put in the magnetic pill for the speedstir, turn it on, put in one scoop dpd powder, then start adding drops until it goes completely clear.

no waiting minutes for anything to change, just doing it in that order to get a result to clear, then dividing the counted drops in half
for a ppm of FC reading.


The chlorine rapidly going away (if it is and you test as I said above) like that could mean 1 of 3 things.

1. the chlorine is not fresh and was stored with sunlight heating it up and losing its potency from the store - possible
2. if you have no cya and the sun is exposed to your pool that will eat it right quick
3. you do have ammonia....in this case getting an aquarium ammonia test kit is your next step.

 

[rio]

Ok, I went to a pet supply store and bought an ammonia-testing kit. I have ammonia - about 5 ppm according to the test result. Go figure. I read in a few other posts that the rule of thumb is add 10x the ammonia amount in chlorine: so I would need to add 50 ppm of chlorine. For my 25k gal pool, using 12.5% sodium hypo, it should be about 10 gallons. Does this sound about right? And how should I dosify this amount?

If, say, it turns out that there is 6 or 7 ppm of ammonia and the amount of chlorine that I add falls short of what's really needed, would it all be in vein? In other words, will the ammonia come back fully unless I kill it 100%?

 

[Poolzzz]

...After testing FC at 2 ppm, I added 2 gallons of 12.5% sodium hypo (this should increase the chlorine in my 25k gallon pool by 10 ppm). 30 minutes later, it still tested 2 ppm.

Similarly, using the daily blue-box method, when I fill it with pool water and add 5 droplets of the yellow stuff, at first the water is light yellow (1-2 ppm). But after sitting for a few minutes it gets much darker. So this goes back to my original question: which should be the more accurate reading, the immediate one, or the one after letting things settle?

Your fc going from 12 to 2 in 30 minutes is basically the ammonia test and indicates presence of ammonia.

Your oto chlorine test showing 2 initially and after a couple minutes getting much darker is telling you there are significant CC's. The OTO test initially shoes FC then after a couple minutes shows TC. The difference in readings are your CC's. You can verify by testing CC with your FAS-DPD test.

These two results together scream ammonia to me.

EDIT: I see you've confirmed it while I was typing. Can you drain you pool and replace water? Might be easier. If you don't put in the full amount of chlorine you'll never be able to hold your FC level. I don't think you have a choice but to go 100%.

 

[proavia]

You're not going to dump all the chlorine in at one time to rid the ammonia.

Treatment for Ammonia:
1. Begin a SLAM and dose FC up to SLAM level. Do not add additional CYA at this point.
2. Retest FC at 10-minute intervals.
a. If FC loss is greater than 50%, add FC to bring back up to SLAM level and continue retesting FC @ 10-minute intervals.
b. IF FC loss is 50% or less, add FC to bring back up to SLAM level. Go to Step 3.
3. If CYA is below 30 ppm, add enough CYA to bring level up to 30 ppm.
4. Continue SLAM as directed in the SLAM article until the SLAM Criteria of Done are met. Test as directed in the SLAM article - no longer need to test FC at 10 minute increments at this point.

 

[borjis]

Your fc going from 12 to 2 in 30 minutes is basically the ammonia test and indicates presence of ammonia.

zero cya will also do that though. an actual ammonia test confirms the presence.
I know he said he has cya, but it's a valid point to consider for others if they read this thread.

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If, say, it turns out that there is 6 or 7 ppm of ammonia and the amount of chlorine that I add falls short of what's really needed, would it all be in vein? In other words, will the ammonia come back fully unless I kill it 100%?

No.

Each time you add the chlorine it will be reducing the amount of ammonia.

 

[rio]

Thanks. Just curious - what would be the downside of going beyond shock level?

- - - Updated - - -

Each time you add the chlorine it will be reducing the amount of ammonia.

That's great to know. Thanks.

 

[Poolzzz]

zero cya will also do that though. an actual ammonia test indicates the presence.

- - - Updated - - -



No.

Each time you add the chlorine it will be reducing the amount of ammonia.

The half life of chlorine with no cya is longer than 30 minutes. So no, zero cya will NOT do that in 30 minutes. Add in the high CCs and is pretty well certain as he found out.

Also stopping short of 100% will not work. It will not hold FC until you reach 100%. You have to either go the whole way or replace water.

 

[rio]

Ok I think there is progress.

I added 12.5 ppm of liquid chlorine. Tested 15 minutes later and got near zero FC.
Added another 12.5 ppm of chlorine. Tested 15 minutes later and got 9 FC and <0.5 CC! Tested ammonia and it showed <0.25 ppm! (At this low end, it's hard to distinguish between 0 and 0.25).
Waited another 20 minutes and tested again, got about 7.5 FC. Ammonia still near zero. So I just added another 5 ppm (to bring to shock level) and I'm waiting to test again shortly. I think I may be about to beat this thing!

But I tested pH and got 7.2 (DOWN from 7.5). I thought liquid chlorine should increase pH? Or could it be that my previous reading of 7.5 would have been faulty given the other conditions?

Thanks for all the help.