Regular DPD test for maintenance - unreliable?

[Gig103]

Hi all,

As the weather warms up, I'm determined NOT to start the season with a green pool as was the norm. I didn't get too lax over the winter and so the sudden increase in chlorine usage is not going to catch me by surprise thanks to everyone here.

My question today is if reagents can go bad? I grabbed my DPD test and got a zero reading for FC. It freaked me out so I pulled out my K2006 (FAS-DPD) and found a reading of 3ppm (pH matched between the two tests). The 'basic' kit is at least a year, if not two, old.

If so, I have to decide if I want to just use my full test a few times a week or replace this kit so I only use the K2006 on the weekends (like I did the second half of last summer once things were in stasis). Your opinions on this would be nice too.

 

[Divin Dave]

There are some of the regents that can go bad after a couple of years.
tftestkits actually has a sale going on this month for regent replacements.

Hi all,

As the weather warms up, I'm determined NOT to start the season with a green pool as was the norm. I didn't get too lax over the winter and so the sudden increase in chlorine usage is not going to catch me by surprise thanks to everyone here.

My question today is if reagents can go bad? I grabbed my DPD test and got a zero reading for FC. It freaked me out so I pulled out my K2006 (FAS-DPD) and found a reading of 3ppm (pH matched between the two tests). The 'basic' kit is at least a year, if not two, old.

If so, I have to decide if I want to just use my full test a few times a week or replace this kit so I only use the K2006 on the weekends (like I did the second half of last summer once things were in stasis). Your opinions on this would be nice too.

 

[BoDarville]

If your basic kit is more than two years old, I would not use those reagents. Plus, depending on where you purchased the basic kit, there's no telling how long it may have been sitting on the store shelf. Given your experiment, I would trust the results of the K2006.

As is the case with the TF-100 kit (what I use), you can purchase the chlorine reagent refills for the K-2006 (the R-0870 powder along with the R-0871 & R-0003 liquid reagents) This is what I do. These reagents will give you everything you need to test chlorine levels (FC, CC, and TC). In fact, there is an XL Option which bundles the R-0870 powder and R-0871 at a cost savings vs. purchasing separately.

 

[Gig103]

So the consensus is to always use the 0870-0871 instead of new DPD? I ask because the tf100 also comes with an oto kit.

 

[JasonLion]

Each of the tests has pros and cons. The OTO test is very quick and simple to use, but essentially only gives you a chorine/no chlorine indication. FAS-DPD is the only one that measures above and FC of 10 and has the best precision, but is also the most work and the most expensive. The DPD test has a limited range and suffers from false negatives (can read zero when the FC level is high). If it had a wider range it might be worth it, but as is it hasn't proven very useful.

If you are SLAMing the pool, you really need the FAS-DPD test.

Many people around here use the OTO kit six days a week just to make sure nothing has gone really wrong, and then use FAS-DPD once a week to get an exact level and figure out dosing. Others prefer to use FAS-DPD all the time.

 

[Divin Dave]

If I wanna absolutely know what my FC is, I use the FAS/DPD. If I want to test for CC, then I can only do this iwth the FAS/DPD
I use the OTO often for the sake of a quick check now and then. Especially in winter time.

Also, many of us and others may well be keeping our FC above 5, because we have SWG's where we recommend higher FC/CYA levels than the OTO can handle. The OTO can only measure up to 5, not above, and the accuracy of it is subjective because of the necessity to compare colors.

OTO also cannot measure CC independently of FC, so the OTO is basically measuring Total Chlorine which in itself isn't exactly indicative of how much FC you have.

So the consensus is to always use the 0870-0871 instead of new DPD? I ask because the tf100 also comes with an oto kit.