First test with FAS-DPD, FC seems very high

scent of a mule · Oct 10, 2012

I recently had a salt water generator installed and got a FAS-DPD kit today. I have been using a Taylor kit without FAS-DPD and my test always read a PPM of about 2 trying to match the pink. With the FAS-DpD test I first filled to 25 ml added two scoops and started titrating. I get to 35 and throw in the towel and decide to use 10ml sample. Again add two scoops and start titrating. 60 drops later it turns clear. Therefore am I reading that my parts per million is 30! If so, why isn't the Taylor standard kit showing up extremely pink and sort of off the chart? BTW CC was
0. I turned down my SWG, but something doesn't seem right.

Swampwoman · Oct 10, 2012

Are you swirling between each drop? Using re- agent r0871?

Maybe try a test with a gallon bucket, calculate the amount of bleach to add for a low ppm, and test your process to confirm. Or just try it on tap water if you have chlorinated water.

scent of a mule · Oct 10, 2012

Tested my tap water. 0.6 ppm.

jblizzle · Oct 10, 2012

I think the pink color match test (DPD) can get bleached out by high FC levels. Do you have a yellow OTO chlorine test? That would look dark yellow/orange if the FC is that high and will not bleach out. I would trust the FAS-DPD.

Posted from my Droid with Tapatalk ... sorry if my response is short

duraleigh · Oct 10, 2012

I would trust the FAS-DPD

Ditto

chem geek · Oct 10, 2012

jblizzle said:
I think the pink color match test (DPD) can get bleached out by high FC levels. Do you have a yellow OTO chlorine test? That would look dark yellow/orange if the FC is that high and will not bleach out. I would trust the FAS-DPD.

This is exactly right. If your OTO test confirms a high FC level, then your DPD test is getting bleached out. This is one of the reasons we recommend the FAS-DPD test since it can accurately measure high chlorine levels.

UnderWaterVanya · Oct 11, 2012

To add more confirmation - here is the Taylor k1001 interferences list. The k1001 has the same DPD test.
http://www.taylortechnologies.com/produ ... KitID=2450

- Sent using Tapatalk

Stuamurr · Oct 11, 2012

the bleach out test with a DPD test can be confirmed by rinsing out the 10ml sample vile and then emptying leaving a couple of drops in the vile, then adding the DPD tablet to the vile and crushing, it should then turn pink, filling the sample vile to the 10ml mark should then bleach out the sample. DPD1 tablets usually bleach out over 10ppm levels. Another suspicion I always have is if the sample vile is not clean, for example I tested the FC in a fish pond after a substantial fill of fresh water, and then discovered that black algae had developed in the vile after testing, so I cleaned the vile with bleach, but it took much cleaning and dilution of the vile before the residual bleach had been removed from the vile, making any future tests invalid until the vile was completely clean.