Confused by TF100 DPD FC numbers

[neato5oh]

Hello,

I'm just getting started and some of my numbers are not making sense. I've had the pool open for a month and I've had the water clear for about a week. I have the pool at 40K gallons because that's what the pool store said it was.

Last night I wanted to shock it so I added 2 gallons of 12.5% bleach. Using the tf100 test with the dpd powder it took 7 drops to clear the solution prior to adding the bleach so 3.5 FC, and then about an hour and a half after adding the stuff it took 32 drops to clear it so 16 FC. These numbers are way off what the pool calculator says. Am I missing something?

I have the CYA at around 35, but I'm not super confident about that test.

 

[Richard320]

40,000 gallons is a HUGE pool. I'd grab a tape measure and start re-calculating volume. The other possibility is that you used the 25 ml sample but multiplied for the 10 ml sample. Which would mean it went from 1.4 to 6.4.

 

[neato5oh]

Def using 10ml.

The pool is a funky shape:
[attachment=0:37nepr4f]pool_sm.jpg[/attachment:37nepr4f]

but it is 48feet long and 18 feet wide at the deep end, and has about a 9 foot deep end and a 4 foot shallow end. Could that be 40K?

 

[jblizzle]

I think 35k-40k could be about right given that information. Have you actually measured the depths? It sure does not look over twice the volume of mine

Mine is about 41 x 14 x 4.5

 

[linen]

I doesn't look that big to me either. Are you certain about your measurements?

Just looking at the pic and guessing, I would guess more like 28000 gallons.

You chemical addition would suggest you are closer to 22000 gallons, though liquid chlorine concentration can not be trusted for pool volume calculations.

 

[neato5oh]

I measured the deep end tonight from the edge of the diving board and it was close to 9'. I wasn't able to reach the deepest part. I'll remeasure the shallow when the FC drops enough to get in, but pretty sure it's about 4'. I put length=48, width=18, deep=9 shallow=4 into a calculator I found for an oval pool and came out with 33K. So I guess it's somewhere above that taking into account the part where it gets wider in the shallow end.