Question about chlorine DPD powder

[spanoob9]

With DPD only drops, it's very important to make sure you're getting well formed drops and that you hold the comparator block up to a bright, uniformly lit background (I use white paper). Indoor lighting is really bad for color rendering.

I have found I can get the two tests to match within a ppm or less difference.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

I had another sorted of unrelated question:

With the CC test regarding MPS interference, I know Taylor makes a reagent to fix it, but without that, how long after adding MPS (say less than an oz) can I test CC without having to worry about the interference?

 

[JoyfulNoise]

I had another sorted of unrelated question:

With the CC test regarding MPS interference, I know Taylor makes a reagent to fix it, but without that, how long after adding MPS (say less than an oz) can I test CC without having to worry about the interference?

The MPS interference is more complicated than that. If you are doing the DPD-FAS test and there is any measurable FC, then the MPS will show up as FC. If there is zero FC, then the MPS interference will show up as CC's. If you are using the DPD-only test for chlorine (like a K-1001), then the MPS will show up as excess CC's.

The amount of MPS you add that affects the test depends on the water volume you are adding it to. If you are adding less than ounce of MPS to a large volume pool, then it probably will not register on the test (nor will it have much effect on the pool). If you are adding a few ounces to a small volume hot tub, then the MPS can have a big effect. MPS reacts a lot more slowly chlorine and so I would expect it to hang around longer if you add MPS in excess of the bather waste that you are trying to oxidize.

If you post up specific information about your use of MPS, then maybe we can answer your concerns better. Typically speaking, MPS is unnecessary except own the most extreme conditions. You're much better off just using chlorine for whatever your application is.

 

[spanoob9]

OK interesting to know..

I have a 500 gallon spa and I typically use a third to half an ounce when I get a strong chlorine smell from it, or when my chlorine demand is high and i don't want to shock so i can go in. I could probably do without out it though.

As far as usage... About 4-6 times a week for 15-40 min. Temp stays at 98 and I raise to 102 during soaks.

I would guess the amount of MPS I've been adding isn't throwing off my tests by too much since i haven't had any problems with sanitizing and the water has been fine with chlorine demand. I'd be interested to know how much of the MPS is showing up in the test, is there a formula I can use?

 

[JoyfulNoise]

OK interesting to know..

I have a 500 gallon spa and I typically use a third to half an ounce when I get a strong chlorine smell from it, or when my chlorine demand is high and i don't want to shock so i can go in. I could probably do without out it though.

As far as usage... About 4-6 times a week for 15-40 min. Temp stays at 98 and I raise to 102 during soaks.

I would guess the amount of MPS I've been adding isn't throwing off my tests by too much since i haven't had any problems with sanitizing and the water has been fine with chlorine demand. I'd be interested to know how much of the MPS is showing up in the test, is there a formula I can use?

If you're getting a "chlorine smell" with the hot tub, then there's probably two issues going on - you are either not adding enough chlorine to oxidize all the bather waste which is generating CCs or you have too much FC to start with and the aeration/evaporation of the spa is causing chlorinated water vapor to hit your nose forming chloramines in your nasal passage.

The figure of merit for spas is this - for every person-hour of bather waste generated in a 104F spa (~500 gallons) it will take 3.5 fl. oz of 8.25% bleach or 7 teaspoons (~1.2 oz) of MPS to oxidize it. There's no easy way to determine a priori how much MPS will be left over if you have both FC and MPS in the water. The only way to know for sure would be to get the MPS Interference Kit (K-2041) so you can measure the total oxidizer concentration and then determine the amount of monopersulfate as equivalent ppm's of chlorine.

However, I would say that your spa is not heavily used and that you could completely eliminate the need for MPS by simply adding enough excess FC AFTER your soaks to oxidize all of the bather waste and leave you with a few ppm's of residual FC. Then, don't add any FC before you soak again (as long as your FC did not drop to 0). I have an attached spa on my pool and so the water in the spa, when I want to use it, has a rather high level of FC (since it's the same water as the pool) to start with. Once the spa gets up to temperature, I found it always to be uncomfortable because of the higher FC level. So what I sometimes do is add peroxide prior to soaking to reduce the FC level and then add a higher level of FC afterwards to oxidize the bather waste (I also add a small amount of muriatic acid prior to soaking to drop the TA in order to keep the pH rise down). By doing this, I find soaking in the spa more comfortable. Another thing you should consider doing is leaving the cover off your spa when you chlorinate it after a soak to ensure that the CCs generated are able to outgas effectively. My attached spa is open all the time so it gets lots of UV and exposure to air to help outgas CCs.

 

[spanoob9]

OK thanks again for the info.

Really the chlorine smell was only a problem when I just got my drop test kit and was still learning. I mainly use it for convenience to put off a chlorine shock for a few days. Gonna cut back on the MPS usage and keep a little on hand for the occasional hot tub party