FAS-DPD Keeps Returning to Pink

Rocket J Squirrel said:

This is normal. The test is over when the solution turns completely colorless. It will return to pink if left to sit.

Further Reading:

FAS-DPD Chlorine Test

The FAS-DPD chlorine test is used to find the level of Free Chlorine in the … Read more…

www.troublefreepool.com

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Huh. I don't recall it doing that in the past.

Thanks!

From the link:

"Continue adding drops until the color changes to clear. The pink color may become extremely faint before it goes away. Make sure that the sample goes completely clear."

And later...

"If left sitting on the counter, the sample will turn pink again one or two minutes after the test is completed. This is normal."

Mine goes completely clear and then begins to turn pink again in maybe 15 seconds or so.

So are you saying the test is over the first moment the solution turns completely colorless?

If so, I would think that would mean one had better complete that CC test within those 15 seconds, wouldn't it?

Mdragger88 said:

I have noticed this happens faster the older/darker the powder is.

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I thought that may have something to do with it. I normally go through a lot of the powder and reagent, so I buy the bulk refills of those when they get low in a newer kit. But don't use those fast enough either.

So I bought a brand new kit just a few months ago. Expiration dates are all quite a ways off.

Oh... also... this phenomenon does not occur with my pool water. I'm going to add this point to the OP.

jseyfert3 said:

How long have you let your pool water sit out after testing? It too should definitely go pink after sitting long enough. May happen faster with the hot tub due to the water being hotter?

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Good question.

I rarely check for CCs in the pool water unless I have good reason. There's almost never a trace in this outdoor, saltwater pool.

But I'd still say I leave it out about the same. And I'm guessing my 15 seconds is generous. May be more like 5 before it goes from crystal clear to a hair pink.

I've been using these kits for 15 years and I test obsessively almost every day. No one I know has anywhere near the water quality I do. And I owe much of that to these forums.

I'm certain I have never witnessed this phenomenon until this summer.

Until I did the SLAM, drain and fill... I had figured there must be some kind of organics or other residue in the tub causing this. But so far, no one has indicated that as a possibility.

So I guess I'll just live with it until the next drain. I'll try just hammering it with a gallon of bleach first.

Also... my Calcium is 30 with no foam... yet. Both water bodies. (vinyl lined pool) Crazy soft water from the city. I'll raise it when I begin to see foam.

Mdragger88 said:

Also be sure to clean your beaker occasionally - alcohol works well. This will remove any residue of cc’s left behind from previous tests.

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Thanks! I'll do that.

However, this is a new kit. And only the pool has been tested for the last few months. Basically no CCs in it. The spa was just reopened last week and the problem resurfaced with this new kit.

I just ran a test:

Granted, the pool is 57F, but I left the beaker sit for 2 minutes after going from red to pink to full clear.

It retained full clarity.

The spa, on the other hand, began to turn pink again within 5 seconds of full clarity. I'd add a drop. Pink in 5 seconds again. Repeated for a total of 4 times. Then it became more like 10 seconds for 2 more rounds of this, then 15 for 2 more... until it finally seemed to quit.

Then I added the 5 drops of CC reagent and got no noticeable change

Then I reran the test adding the 5 CC drops as quickly as I could right after it went clear. But I could see it turning by the time I picked up the bottle. It went pink. Then I added 1 drop of reagent it went back to that real faint pink that it's been doing all along without adding CC drops.

So... do I have 0.5 or less of CCs?

Or...?

FC was 6.0
CYA 35

So just right according to Pool Math