K-1000 vs DPD Test

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BIC

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Jul 7, 2007
108
Hey,

I have almost never used the DPD test, but because of some problems this year I started to use it in order to get precise FC reading. My problem is that DPD and K-1000 kit give me very different numbers.

For instance: this morning when I tested with DPD it tells me I have 9 FC (18 drops) and .5 CC (1 drop). I then tested it with my K-1000 Kit and I get 4 FC.

Is DPD reliable only when shocking the pool (high numbers like 30 and more) or is it also precise in the low numbers like 2 to 5 FC? Why do I have a big difference like that? Which one is the good number?

Note: my DPD powder and liquid are at their third season (they should still be good I think), my K-1000 is brand new.

Any comments?

BIC
 
Well, how old are your kits? Are you sure they were fresh when you bought them?

I test my TF kit against the Walmart HTH 6-way and another test strip and so far, the only difference I see in my tests are the TA. The TA always reads higher with the TF kit.
 
BIC said:
Note: my DPD powder and liquid are at their third season (they should still be good I think), my K-1000 is brand new.
Click to expand...

buggs: have you seen the thing about wiping the TA reagent bottle (from the tf100) with a damp tissue between drops? sometimes that bottle has a static electricity build up which causes smaller drops and higher readings.
 
BIC,

The test you have is an FAS/DPD. The DPD test is substantially different.

Use the OTO test to test for the presence of chlorine......it's very dependable but it's not very precise.

Use your FAS/DPD test to test for a precise amount of FC/CC....it's very accurate.
 
It sounds like you mean the FAS-DPD chlorine test every time you say DPD. The FAS-DPD chlorine test has you add some powder to turn the sample pink and then count drops till it turns clear again. The DPD test has you add drops to turn the sample various shades of red which is then compared to a color chart.

The Taylor K-1000 test includes an OTO chlorine test. The OTO test is very difficult to read correctly for chlorine levels above 2, and it doesn't measure levels above 5. Also, the OTO test measures TC, while the FAS-DPD test measures FC and CC separately.

The FAS-DPD test is always more precise, both at high FC levels and at low FC levels. The OTO test is handy because it is quick and easy, and it is reasonably precise for TC levels between 0 and 2. Many people use the OTO test just for a quick "chlorine"/"no chlorine" check, without expecting it to give a precise level.
 
How long are you letting the OTO test sit? It only measures total chlorine and most people do not realize that it needs to sit for about 3-5 minues to fully develop.
Also, are you usng a 10 ml sample size or a 25 ml sample size with the FAS-DPD test?
If you are using a 10 ml sample size then 18 drops is 9 ppm FC + 1 drop for the CC = .5 ppm CC = 9.5 ppm TC.
For 25 ml sample 18 drops is 3.6 ppm FC + 1 drop CC = .2 ppm CC = 3.8 ppm TC
3.8 ppm TC is about what you said you were getting on the OTO test.
 
Here are some answers to questins that were asked:
- I use the Trouble Free Test Kit (TF-100) for my FAS-DPD test. This is my third season (season = May to September) with thaty kit. It was always kept indoor (house), in a warm place and not exposed to sun light. I use the 10ml sample size as indicated in the TF-100 Kit.
- My OTO chlorine test is done with my brand new (first season) K-1000F (F = Frencn). I ddin't know it had to sit for 3-5 mins before reading (not in the instructions included with TF-100). I will do that from now on.

More info about the pool problem this year:
- This is my third season having a pool, I learned almost everything I know here :)

- During my two first seasons I have never shocked the pool and never had algae. The micro shocks happening in the cell (when generating chlorine) were doing the job I guess (instead of shocking the pool weekly).

- This season I always have some deposits of green sand at the bottom of the pool (algae I guess).

- During the two first seasons, I noticed that when the cell was generating chlorine it made a bubble noise (7up) that I could hear from under the water. Plus, I could see (when generatong chlorine) a cloud of bubbles coming out of the water return. This year I still hear the noise (when generating chlorine), but I do not see a big cloud of bubbles (just a bit of bubble) coming out of the water return. Is my cell getting old (third season)?

- During the two first seasons I used to set my cell between 15-25% for 12h/day (pump on) and would always get 4ppm during the day and a very crystal clear water. This year I have to let it run for 24h/day and set it to higher level (30-40%) to still get (from OTO test) 4 ppm (DPD-Fast says higher number, pool store says 4ppm). My water is not as clear as the first two years. This is why I now test with DPD-Fast (that gives me 9ppm with 10ml sample). Again, is my cell getting old and not working properly?

- Two days ago, even if the cell didn't look too dirty, I decided to clean it (for the first time) with a product meant for that from TABEX. Since that, I didn't look under the water to see if there is more bubbles now coming out of the water return when it is generating chlorine.

- It seems now, that if I don't shock the pool weekly I will get green sand deposite at the bottom of the pool. when I shock the pool (with liquid chlorine), the water gets clear and the green deposites will only come back in around 7-10 days :|

I'm starting to think that the cell does not shock the pool enough (micro shocks are weaker) anynmore and that I have to shock the pool myselft to get clear water and no green sand deposites.

This is the story behind why I started to test with DPD-fast and saw the difference with OTO test. So:

1) why the difference between the two test? I will test with a 3-5 mins sit today and see how it goes. I will also return to the pool store to see what they read (they use Taylor drops to test).

2) why do I have problem (green sand) with my water this year? Is my cell (third season: May to September) getting tired/old?

Am I going nuts with all those green sand deposites, 7up bubbles and high ppm reading stories? :?

BIC
 
If you are getting dead algae accumulating on the bottom of the pool, you have too little FC in the pool, and you need to increase the percentage on the SWG.

The FAS-DPD test is by far the best available chlorine test. Everything else is inferior. The OTO test is the least expensive test and only gives approximate results. Still, the OTO test is handy for many situations, despite it's approximate readings.
 
JasonLion said:
If you are getting dead algae accumulating on the bottom of the pool, you have too little FC in the pool, and you need to increase the percentage on the SWG.

The FAS-DPD test is by far the best available chlorine test. Everything else is inferior. The OTO test is the least expensive test and only gives approximate results. Still, the OTO test is handy for many situations, despite it's approximate readings.
Click to expand...

Hi
Jason,

If I trust my DPD-Fast Test, it says I have 9 ppm (FC) and 0.5 (CC), so I should have enough. I have around 60 for Stabilizer. I shouldn't need more than 9 ppm for FC. Am I missing something?

I also want to add that I cleaned my filter sand by pouring a liquid (sand clenaer) in the Skimmer while doing a backwash (the pool store told me to try that). I have no idea if it does a good job, but my filter is just at its third season.

BIC
 

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If your FC level is consistently 9, then you shouldn't be having a problem with algae. Have you watched the FC level over time? You said that you only get the "green sand" on the bottom of the pool some of the time.

Filter cleaner is almost always a waste of money, but it shouldn't hurt anything.
 
JasonLion said:
If your FC level is consistently 9, then you shouldn't be having a problem with algae. Have you watched the FC level over time? You said that you only get the "green sand" on the bottom of the pool some of the time.
Click to expand...

I always check my FC every two days with OTO. Based on my OTO test, it was always 3+, so it ashould be ok. My DPD-Fast gives me higher numbers, so in both cases it should be ok.

The fact that I have to put my SWG higher (30-40%) is telling me that the micro shocks are not as strong as they were in the two first seasons, it maybe doesn't generate as much chlorine per hour that it was in the first two seasons. So maybe now I have to shock the pool every week like pool maintained with Granular chlorine. If I don't shock my water is not very clear and I get green sand.

People that do not use SWG, but granular chlorine, tell me that even if they have 3+ ppm all the time, they will get algea if they don't shock their pool, ..... so it is almost my case.

What do you think?

BIC
 
Sounds like you need to perform an overnight FC loss test , with swg off, with your FAS/DPD test and report back the results...it could just be that your SWG is just constantly keeping up with blooming algae.

Go ahead an post a full set of fresh test results also. 60ppm on CYA is slightly on the low end of what is recommended for a SWG.

Also, I know the FAS/DPD is more expensive than the OTO, but until this clears I would perform the FAS/DPD tests daily and disregard your k-1000 OTO results. The OTO is really not that accurate and is only helpful for testing the presence of chlorine...I know I can't tell the difference in color from 2ppm to 5ppm :oops:

Good luck
 
frustratedpoolmom,

What I call "micro shocks" are the little shocks (electrolyse or something like that) that the SWG cell gives to the water in order to generate the chlorine from the salt. These mini-shocks are happening in the cell multiple times and can be seen as a process similar to shocking a pool but at a micro level (after one shock, there is lots of chlorine generated instantly into the cell, so it purifies the water present in the cell at that specific time). If there is hundreds (or more) micro shocks happeneing in the SWG cell over a certain period (many hours, a day or even a week) it kinds of shock the entire pool. This is one explaination to "why pool using SWG do not need to be shocked", the cell does the job. At least this is what I belive :wink: There is experts here on the site that could explain this better than me.... or they could contradic my theory :( I just think this explaination makes sense for me, but I'm not an expert at all. :|

To everyone :mrgreen: ,

I shocked the pool yesterday night (bleach 5L), the pump ran all night and day. Tonight I have FC=13 and CC= 0.5 :| Should I shock the pool again tonight or just tomorrow morning if I have FC < 13?

Nobody kind of think the theory that my cell is getting weak/old and that is why I have to shock the pool now (never shock the pool in the past seasons)?

BIC
 
I see what you're saying with "microshocks", but afaik that has nothing to do with having to shock. no one should have to shock who follows the chlorine/cya method, and has good filtration, circulation and brushing.
to determine if you're done shocking you need to do the overnight fc loss test as seen in pool school.
here is some good info on swg "microshocks", chemgeek's post in particular.
ever-know-of-anyone-who-doesn-t-like-a-swcg-pool-t1235-20.html
as far as your cell, couldn't tell you.
 

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