A little confused by the behaviour of the FC/CC test

[dogsbody]

By guess and by golly I managed to pin the CYA to a reasonable level - 45ppm - though I don't
know how it's going to hold up, as some new leaks (grrr...) have appeared that are going to require
a little periodic topping-up, as I don't want to deal with them before spring. But that's not the
question.

I do the Taylor FAS-DPD test; takes three dippers to light up the 25ml sample, which seems okay.
Start adding the R-0871, and it goes clear in two or three drops, which I gather is a little on the low
side for FC, but approaching the zone. But while I'm off fetching my notebook and pencil so I can
log what's going on... it turns pink again, and it takes a couple of more drops to dismiss it. I've
repeated this (minus the notebook/pencil part) a few times, and I'm wondering what's causing it.
Which reading can/should I trust? And why's it happening?

 

[PoolStored]

Your fc is .4. (2 drops in 25ml). This is nowhere close to in range. Follow this->FC/CYA Levels

You should immediately go to CC test without delay. The pink coming back is normal if you let it sit. Ignore it.

 

[dogsbody]

What I meant was "low but measurable".

On the question, thanks - stick with the first reading. Can anyone explain why this happens?

 

[PoolStored]

Can anyone explain why this happens?

There might be a slight excess of DPD reagent left in the sample

 

[dogsbody]

Ah, and it's taking its time dissolving.

 

[Bperry]

Ah, and it's taking its time dissolving.

You also only need two scoops of powder. That’ll save on reagent.

Also if you switch to 10ml sample and multiply the drops by 0.5, it’ll save even more and be plenty accurate, and be easier math to get the number.

 

[dogsbody]

Yes, I did read the instructions.