Can bleach used help calc total volume?

UnderWaterVanya

TFP Expert
LifeTime Supporter
Jun 14, 2012
2,589
Mint Hill, NC
#1
I have not yet had time to shock the pool fully since I started working with this pool about a week ago. I finally had time to crank it up and after measuring 5.5ppm I checked pool calculator and came up with 315oz of 6% bleach to raise this to a shock level of around 15 - this assumed a pool with around 16000 gallons. The bleach I'm using is a Food Lion generic of some type that claims 6%. I decided to dump a full 364oz of bleach in since I was not 100% positive of my CYA measurement and I was OK if the shock was a little higher. The predicted increase was 11ppm for a total of 16.5ppm expected.

Two hours after loading the pool with the bleach (loaded at 10:30pm, collected sample at 12:45am, finished up with tests around 1:10am) I had a starting OCLT value of 19.5ppm FC. Looking into this further I figured out that in order to get the 14ppm increase in FC I needed to have a pool of about 13000 gallons - or bleach that was stronger than 6%.

Given the fact that the pool is roughly 16x32 with a shallow depth of 3' and a deep end depth of 5.75', and the fact that the pool has sloping sides that get narrower as the pool gets deeper, and the pool also has rounded corners but is otherwise rectangular I had expected closer to 15500 gallons or 16000 gallons. (I'll try to upload a picture soon).

Oh as for the OCLT - not great.

1am results:
FC: 19.5
CC: 0.5
Ph: 8? (> 7.8 < 8.2) (Before adding the Bleach this was 7.5 - I suspect false result due to high FC)
CYA: 45? (Tested indoors at night by flourescent light)
TA: Not tested, last test 175, test strips (which have been fairly accurate) shows around 180.
CH: Not tested, last test 350 - no fill water or rain since, minimal evaporation.

9am results (no sun on pool at 9am)
FC: 18.0
CC: 0.5
Ph: Not Tested, Test Strip shows 8.2 - same as last night, high FC false expected
CYA: Not Tested - no change in this expected
TA: Not tested, Test Strip shows 180'ish still
CH: Not Tested see above.

So I've lost 1.5ppm of FC overnight. <sigh> Guess I have to keep shocking. At my CYA level I was going to shoot for 16ppm or a slight overshoot. The pool is 5 mins from my house where I am working from home today. However I'm busy off and on all day without flexibility to drive back and forth willy nilly. I figured I'd check again sometime around lunch and add more bleach if needed then and again this evening. My expectation is that over the day I will lose another 1.5ppm in Organics consumption, and 3-5ppm in Sunlight losses. So I am expecting to need to raise the FC back up around 1pm by 3-5ppm keeping it around 19-20ppm mid-day and then expecting a night measurement of around 16ppm.

Is this a good plan?
 

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
22,818
SouthWest Alabama
#2
You can use bleach additions to get a better estimate on the volume but don't put much faith in one addition. Measure through several additions and if you're constantly overshooting then adjust the volume down to where it's closer to the expected change.

Just to note; I get between 13,000 and 14,000 gallons for a pool that size.

If there was absolutely no sun on the pool at 9 am then you need to shock. However, it's hard to believe that there was absolutely no sun on the pool at that time of morning.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,322
San Dimas, CA (LA County)
#4
Yes, it can, but it will take several weeks to pin it down. AND it requires accurate readings - test strips and color blocks will not work for this purpose; you need a FAS-DPD test that can measure down to .2ppm.

Besides bleach, acid will also help you calculate the volume. Both pH changes and TA changes.

In either case, if you come up short of the expected results, next time raise the volume on the pool calculator by 500 gallons. If you overshoot, reduce it. Keep fine-tuning it. When the results match the expected results, you'll have your volume within a hundred gallons or so, which is close enough.
 

CaOCl2

LifeTime Supporter
May 23, 2007
326
Montreal Canada
#5
If you use bleach for this you need to know that it hasn't degraded and what the actual chlorine content is (it may be different that what's indicated on the label). You also need to be precise in measuring the quantity of bleach you're adding. Better to use a weighted amount of something like 75% cal-hypo. Measure the FC (to 0.2 ppm) at sunset, add the cal-hypo, let it circulate, calculate the rise in FC and work out the math.
 

UnderWaterVanya

TFP Expert
LifeTime Supporter
Jun 14, 2012
2,589
Mint Hill, NC
#6
Bama Rambler said:
You can use bleach additions to get a better estimate on the volume but don't put much faith in one addition. Measure through several additions and if you're constantly overshooting then adjust the volume down to where it's closer to the expected change.

Just to note; I get between 13,000 and 14,000 gallons for a pool that size.

If there was absolutely no sun on the pool at 9 am then you need to shock. However, it's hard to believe that there was absolutely no sun on the pool at that time of morning.
Zero sun - tall trees on the side towards the rising sun. Might be sun free until 10am not sure since I live 1.5 miles from the house.
Thanks for confirmation on the sizing. I'm going to use 13500 for my basic calculations for a while and see how this works.
 

UnderWaterVanya

TFP Expert
LifeTime Supporter
Jun 14, 2012
2,589
Mint Hill, NC
#7
Richard320 said:
Yes, it can, but it will take several weeks to pin it down. AND it requires accurate readings - test strips and color blocks will not work for this purpose; you need a FAS-DPD test that can measure down to .2ppm.

Besides bleach, acid will also help you calculate the volume. Both pH changes and TA changes.

In either case, if you come up short of the expected results, next time raise the volume on the pool calculator by 500 gallons. If you overshoot, reduce it. Keep fine-tuning it. When the results match the expected results, you'll have your volume within a hundred gallons or so, which is close enough.
Sorry - I wasn't clear. I used my TFT-100 kit and test strips. I'm surprised how accurate my test strips have been - they are crude but they are reasonably accurate so far. Being able to cross compare them with the kit helps me know that if I need a quick check I can use them to get crude data. I used the 10ml sample with the FAS-DPD kit so I only had 0.5ppm accuracy. Do I need the 0.2ppm for the OCLT? I thought 0.5ppm was sufficient?
 

UnderWaterVanya

TFP Expert
LifeTime Supporter
Jun 14, 2012
2,589
Mint Hill, NC
#8
Is it safe for my kids to swim at 18ppm? The "shock value" seems closer to 16ppm - but I think I remember that even the mustard shock level is safe which is higher - is that accurate?

Also what is the basis for this view? I know that experience shows this is correct for many here - is there any other data that shows that it is OK to swim at these levels?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,322
San Dimas, CA (LA County)
#9
UnderWaterVanya said:
Richard320 said:
Yes, it can, but it will take several weeks to pin it down. AND it requires accurate readings - test strips and color blocks will not work for this purpose; you need a FAS-DPD test that can measure down to .2ppm.

Besides bleach, acid will also help you calculate the volume. Both pH changes and TA changes.

In either case, if you come up short of the expected results, next time raise the volume on the pool calculator by 500 gallons. If you overshoot, reduce it. Keep fine-tuning it. When the results match the expected results, you'll have your volume within a hundred gallons or so, which is close enough.
Sorry - I wasn't clear. I used my TFT-100 kit and test strips. I'm surprised how accurate my test strips have been - they are crude but they are reasonably accurate so far. Being able to cross compare them with the kit helps me know that if I need a quick check I can use them to get crude data. I used the 10ml sample with the FAS-DPD kit so I only had 0.5ppm accuracy. Do I need the 0.2ppm for the OCLT? I thought 0.5ppm was sufficient?
For overnight test, it's fine. I thought you wanted to calculate volume.
 

UnderWaterVanya

TFP Expert
LifeTime Supporter
Jun 14, 2012
2,589
Mint Hill, NC
#10
Richard320 said:
UnderWaterVanya said:
Richard320 said:
Yes, it can, but it will take several weeks to pin it down. AND it requires accurate readings - test strips and color blocks will not work for this purpose; you need a FAS-DPD test that can measure down to .2ppm.

Besides bleach, acid will also help you calculate the volume. Both pH changes and TA changes.

In either case, if you come up short of the expected results, next time raise the volume on the pool calculator by 500 gallons. If you overshoot, reduce it. Keep fine-tuning it. When the results match the expected results, you'll have your volume within a hundred gallons or so, which is close enough.
Sorry - I wasn't clear. I used my TFT-100 kit and test strips. I'm surprised how accurate my test strips have been - they are crude but they are reasonably accurate so far. Being able to cross compare them with the kit helps me know that if I need a quick check I can use them to get crude data. I used the 10ml sample with the FAS-DPD kit so I only had 0.5ppm accuracy. Do I need the 0.2ppm for the OCLT? I thought 0.5ppm was sufficient?
For overnight test, it's fine. I thought you wanted to calculate volume.
LOL - I'm mixing too many meanings. Yes I am trying to get a basic estimate of volume - I'm going to watch what happens with all of the chemicals over time and see what the inferred volume appears to be. I think you are saying that 0.2ppm testing (25ml) would be more accurate if I want more exacting volume estimation. I see your point - but the way I am getting my estimates reverse engineered (Poolcalculator.com) isn't as precise as that. I can adjust the volume in 500gallon increments and the projected FC doesn't change. I'm not sure it's not limited to 1ppm in the estimation section at the bottom.