Higher chlorine than expected

[jblizzle]

Warning ... this is a bit long.

Background:
Recently moved into a house with a 30+ yo pool that needed redone, drained it and installed pebblesheen, new tile, new skimmer, new auto-fill and new Kool decking. Got 3 months of pool service included in the project that just ran out ... so time to start following the great advice found here.

I had estimated the volume of the pool to be 20-25k when I drained it. A few weeks ago added some salt. Before I had 400ppm (Taylor drop test) added 4-40lb bags and measured 1400ppm added 2 more bags and measured 1900. So, based on the Pool Calculator I must be around 20k gal ... a bit lower than I expected given how large the pool looks (I guess it is just shallow)

Issue:
Had a party on Saturday with lots of people in the pool. In the early evening I measured my chemistry (using the TF100 kit):

Temp: 85
FC: 8
CC: 0.5
pH: 7.5
TA: 100
CH: 350
CYA: 100 (seems way high ... thanks pool company; although planning on eventually switching to SWG so this may not be too bad)

Looks pretty good, but worried about the high load that day and planned to go get some bleach.

Tuesday morning measure again (Is "it is over 100 degrees out" a good enough excuse as to why I did not test on Sun and Mon?):
FC: 3.5
CC: 0
Rest the same

OOPS need to get that bleach.

Pickup some bleach on way home and Tuesday night measure again:
FC: 2.5
CC: 0

Check out Pool Calculator for 20k gallon (recommends 8-13) from FC 2.5 to get up to about 11 calls for just about 2-182oz 6% Walmart Bleach. Turn on pump. Add the 2 bottles of bleach. Come back 1 hour later and remeasure:
FC: 15.0
CC: 0

WHAT?

Figure maybe it was not fully mixed and I sampled in a high location. Measure this morning:
FC: 13.5
CC: 0

Still higher than I would have thought I should have gotten. Just wondering if I am missing something or what might explain the higher than expected FC.

Thanks. You have all been so helpful to me already and you did not even know it.

 

[Bama Rambler]

Sounds like your pool may be smaller than you think or the % bleach may be higher or some combination of the two.

 

[jblizzle]

I admit that I may not know the size exactly, but I can not see how my estimate could be that far off ... based on simple volume calculations and my salt level measurements.

Has anyone else ever found the Walmart bleach to be > 6%?

Maybe it could be explained by my starting measurement being low, after measurement being high, pool volume actually lower and the bleach > 6% ... but being an engineer ... that seems like an awful lot of stars to align.

 

[waskydiver]

Don't know what to say...

Your numbers look about right.

Not to pick nits, but the salt test would have given you more like 19,200 gallons. But, yea... we're estimating parts per million... yea... 20,000 close enough.

I guess with the auto-fill we are not talking about water loss from the test.

I would probably just say that when it's time to add bleach again to dial down your pool size a bit further... I think about 18,000 would be a good place to start.

The idea that I follow is not to know what exact numbers to plug in and becoming a slave to the pool calculator. I just try to get to the point where I take my chlorine reading on a daily basis, and when I look at the results be like: "Well, that's a four 'glugger'. But, it's gonna rain tonight, better give it an extra 'glug'".

 

[jblizzle]

"Well, that's a four 'glugger'. But, it's gonna rain tonight, better give it an extra 'glug'".

LOL ... I think this is kind of the direction I would like to head as well ... just have to suppress the engineer in me.