K-2006 test kit, just a few thoughts

[BigDave]

I also use only one scoop. My shampoo instructions say wash, rinse, and repeat. I only repeat if my hair doesn't feel clean after the first one. I'm a maverick.

[BigTallGuy]

The DPD dye is the same, but the powder has some advantages. The liquid DPD is subject to oxidation from oxygen and the reagents attempt to reduce this problem by having the pH of the dye solution be a bit lower and by adding EDTA to the solution and there are also phosphate buffers. There are side effects with the liquid DPD solutions that can occur depending on the pool water sample, such as having the sample be high in calcium which can precipitate as calcium phosphate. The powdered DPD is far less susceptible to oxidation from oxygen and requires less buffering and EDTA as a result.

So if you are in a pinch and don't have any powder available, you can use the DPD liquid instead. It's still more accurate to titrate with the FAS-DPD drops regardless of which form of DPD indicator dye you use.

So I assume then that the DPD TABLETS in the individual foil blister packs are the same as the powder, only in a tablet form, and the size of the tablet (dosage) is of no consequence just as two vs. one scoops is, Correct?

[lstinthot]

So if there is no Cl` in the pool will adding more than 2 drop make the water change eventually? I did not go past 2 scoops as i was expecting to have very low Cl` levels.

Thanks

[Watermom]

No. If you get no pink color with two scoops of powder, then you have no chlorine in the pool. No need to add more powder -- will just waste it.

[chem geek]

If the chlorine level was very high, then you'd see a flash of pink when adding the scoops of powder, even if after two scoops it went clear. I've never determined exactly how much FC wipes out each scoop of powder, but I'm guessing that to have it stay clear with 2 scoops it would probably have to be quite high such as 40 or more ppm, though that's just a guess.

[waterbear]

So I assume then that the DPD TABLETS in the individual foil blister packs are the same as the powder, only in a tablet form, and the size of the tablet (dosage) is of no consequence just as two vs. one scoops is, Correct?

not exactly. Taylor DPD powder is a proprietary, buffered mixture

[waterbear]

So if there is no Cl` in the pool will adding more than 2 drop make the water change eventually? I did not go past 2 scoops as i was expecting to have very low Cl` levels.

Thanks

If there is no chlorine then there will be no pink color. the pink color (known as Wurster dye or Wurster's Red) is caused by a chemical reaction between the DPD and an oxidizer. If there are very high levels then the reaction proceeds further and forms a colorless Imine, hence the "flash" of pink as the Worster's Red forms and then disappears as it is further oxidized to the Imine. Adding more DPD powder will then react with the now lower level of remaining chlorine and the pink Wurster dye can form again and you can procede with the titration. The acutal AMOUNT of DPD powder used is not that important as long as you have enough to form the Worster's Red dye. If it only takes one scoop that is fine. If it takes 3 or 4 because of high FC that is fine. At very very high FC levels a yellow free radical is formed instead of Wurster's Red or Imine and that means the FC is too high to titrate.

[BigTallGuy]

not exactly. Taylor DPD powder is a proprietary, buffered mixture

Thanks Evan. The one scoop and not having to worry about the exact amount is much better than buying the tablets. I was just curious and was trying to make the testing a little more repeatable.

[lstinthot]

Thanks for the explanation. I have been enjoying my test kit the last couple of days. Water is looking good now that I know a little more about what I am doing and not relying on the hockey pucks.

[stlbill]

I have one of these powder dispensers and love it. It fits on the container very snug so I am not sure why it cannot be left on the container. I leave mine on for faster testing and haven't had any issues.