DPD 870 Powder not dissolving

[Dantart]

My pool is pretty cold, around 53 degrees. When I add my DPD powder (870) it doesn't turn a color and barely dissolves. There are clumps of it at the bottom of the tube.
I used this powder two days ago and it worked fine. Water was a bit warmer though. Any ideas or help would be appreciated.
Thanks

 

[ajw22]

Take your test sample inside and let it warm up to room temp.

If the power does not cause the sample to change color then your FC is 0.

I think you need to add some LC to your pool.

 

[JoyfulNoise]

It’s actually ok if there’s a small amount undissolved. The powder is actually a mixture of about 5 different chemical components and one of them is a pH buffer that slowly dissolves especially if it’s course grained. It’s totally ok from a chemistry standpoint as the DPD indicator is only a very tiny percentage of the mixture (like 1 or 2% by weight). The DPD dissolves rapidly.

 

[Dantart]

Ok, thank you. It seems strange, they opened my pool on Friday and added 4 gallons of LC, 10%. I checked it late on Saturday and the FC was 7. Today on Sunday it showed 0. I just added a gallon of 10% so I will see what it reads tomorrow. Water temp is pretty cold.

 

[V___25]

I find I have to let my water come up to at least 60 to get good results. Also, if you don't have one, the speed stir helps with getting that powder to dissolve better than swirling. And with the light on the bottom, you can see how much is dissolved or still floating in chunks.

 

[Turbo1Ton]

I just added a gallon of 10% so I will see what it reads tomorrow. Water temp is pretty cold.

In the future, it is best to test after 30 minutes of mixing, or so, to confirm your addition was what you expected. Waiting a day, you don't know if your LC was weaker than advertised, or if there are organics causing the FC to be consumed.

--Jeff

 

[Dantart]

Thank you for all there helpful info. I am a fairly new pool owner. 15,000 Gallon vinyl liner in ground pool installed in 2021. Last year about August my CYA got really high. They had to replace my liner this year because it was defective so I got new water. I was going to try and not use tabs and only use LC. However, I am getting a little nervous that I may have to add so much every few days it won't be cost prohibitive. I was also told that you could use both to some degree. I just want to avoid the high CYA issue I had last year. The water is so cold right now that I am not sure how accurate my tests are.

 

[MITBeta]

You can use any chlorine products you want to sanitize your pool as long as you know what you're getting in addition to the chlorine (calcium, stabilizer, salt, etc.). The best way to do that is to know what's already in your pool by using a great test kit (Test Kits Compared) and PoolMath to know what and how much you're adding.

I have found that the cost of liquid chlorine is less than any other product on a $/ppm basis.

 

[AK-]

For 15K gallons to add 4.5ppm of FC you going to need about 2/3 of 10% gallon of LC. Using Trichlor you need abou 1.25 tablets for the same 4.5 ppm of chlorine.

You can get 10% LC at Walmart for $4.60/gallon, so about $3.07/day.
I found a 30lb bucket of Trichlor on BJs at $160 (lowest I seen this year), so about $2.67/tablet or $3.34/day.

By using LC you save in drain/refill water.

Note: 4.5ppm was my daily consumption on peak summer .