Gallon Issue??

[alanrmeadows]

I'm certain that my fiberglass pool is at minimum 15'8" X 34"...it is pretty much rectangular, has at least an 8ft. deep end and 3ft. shallow end. The sides are sloping in the deep end. When I do my calculations on the pool calculator...I keep backing into the calculation that I have approx. a 15,300 gallon pool. Is there anyway this is possible?? I was at 12 FC and was trying to get to 15 (based on the assumption of a 22,400 gallon pool). When I added 1 gallon and 1 cup as directed and waited for an hour, my new reading was 16.5-17.00. The only way to reconcile that increase using the same amount of chemical was to lower my gallons to 15,300. Something doesn't seem right?? Surely the pool is larger and closer to 20,000 based on the measurments?

Thanks,
Alan

 

[Bama Rambler]

When I figure it I get about 18,000 gallons and if the corners are rounded and the slopes wider then it's certainly possible that it's close to 15,000 gallons. Water volume will fool you and most people have a tendency to over estimate it.

 

[PaulR]

If you told the pool calculator you were using 6% bleach for 22,400 gallons, I also get 1 gallon 1 cup.
If you then added that much 10% bleach instead of 6%, I get an FC increase of 4.8 instead of 3.

If it really was 6% bleach, the chems don't lie... in fact that's one of the usual ways to measure the volume of an irregularly shaped pool, add a known quantity of something that will be easy to measure (like bleach), and see how much effect it has.
--paulr

 

[Richard320]

I can think of a few things you may have forgotten to take into account.

You might be measuring pool depth rather than water depth.
The sides may slope more steeply than you think.
The bottom may be flat in the shallow end and then slope rather than an even slope from end to end.
You may have forgotten to deduct for things like steps and swim shelves. I have one that displaces about 900 gallons. There's 7.48 gallons in a cubic foot.

And going the other way, there's some water in the lines and filter.

 

[alanrmeadows]

I'm starting to either feel real dumb or real frustrated...or both. I know how to perform titration tests...I did them throughout college. Here's the deal...yesterday I backed into a calculation (using bleach) that determined that I had 17,000 gallons. I mean I was right on...I was able to produce an exact FC number using the recommended bleach at 17,000 gallons. This morning, after doing a test and determining my FC was 13.5, I added enough bleach to raise it to what I thought was 19. When I tested it 1.5 hours later, it was at 22.5. The calculator says that should happen with a 10,000 gallon pool. What is going on? Is there not a way to get an accurate volume measurement?? This is driving me crazy!!

Thanks,
Alan

 

[PaulR]

Where are you getting your bleach? The calculations are assuming a particular strength of the bleach you add, and if that varies somewhat, your results will be off.

If you have a big bucket you test your bleach this way: Put 4 gallons water into the bucket. If you don't know it's chlorine-free (e.g. tap water), test the FC. Add 1/2 tsp bleach, mix thoroughly. Test FC again. If it's 6% bleach the FC should go up by 10.

Or if you're more comfortable with metric, add 1ml bleach per 10L water, and the FC rise should equal the % hypochlorite.
--paulr

 

[alanrmeadows]

Paulr,
I get my bleach at Home Depot and the strength is 6.15%. I put 6.15% in the pool calculator for my calculations. Any other ideas to determine accurate volume?

Thanks,
Alan

 

[PaulR]

You are using the same test kit and reagents (and test personnel ) each time, so if you're getting different results from different attempts to measure volume with the bleach method, that leaves two distinct sources of error: The strength of the particular jug of bleach you're using, or measurement error on the part of the tester.

There's an extent to which it doesn't really matter that much. You shoot for 19 and get 22, big deal. On the other hand, for myself I like to know, so I can sympathize if you do too. And you can just do what I did: (1) pick a number and use that for a while. (2) keep track of whether you consistently undershoot or overshoot. (3) if the difference is consistent, revise the volume number and repeat. You were using 22400 and always overshooting, so now you pick a smaller number and see how that goes for a while. Eventually it will converge on a number you can be happy with.
--paulr

 

[alanrmeadows]

Paulr,
I like your response...I'm a perfectionist and need someone to calm me down at times.

Thanks,
Alan

 

[alanrmeadows]

OK...I'm very frustrated again. I tested FC at 7:00pm and it was 19. I wanted to raise it to 22 in my supposedly 17,000 gallon pool. The Pool Calculator called for 3 quarts and 1 cup. I used a measuring device that measured my 6.15% bleach from Home Depot very precisely. I checked again at 9:00 and IT WAS 26! That correlates to a 7,100 gallon pool which makes absolutely no sense. I made triple certain that the bottom of the meniscus was on 10mL both times. I'm lost and frankly don't have a clue! Does the size of the "heaping scoop" of powder matter? Is there any other way to determine my gallons...can I pay someone to come out and get close. I hate to consider this trouble free stuff when I obviously can't even tell you what size pool I have. I'm through venting for the evening!

Thanks,
Alan

 

[frustratedpoolmom]

Are you using the small scoop end to dispense the powder, or are you using the flat-handled end?

 

[alanrmeadows]

I'm using the small scoop end.

Alan

 

[JasonLion]

It sounds to me like either your measuring cup is way off or that bleach is much stronger than it is labeled. Finding bleach as strong as 8% in bottles labeled as 6% is possible, though rare.

 

[todd.scallions]

Based on this post, I was way under estimating how many gallons I am working with in my 18ft x 36ft rectangle pool. I don't even know how I originally came up with 24,500! I did 18x36x6x7.5=29,160 (width X length X average depth X one cubic ft of water = ) I just rounded up to 30,000 to compensate for the water in the lines & pump. Wow, looks like I gonna need a bigger supply of bleach!

 

[PaulR]

Does the size of the "heaping scoop" of powder matter?

Taylor says to use two level scoops, which the TF100 simplifies to one heaping scoop. The precise amount of powder doesn't matter that much, as long as it's "enough." I'd say, don't skimp on the heap, but don't feel like it has to be as big as you can make it either.
--paulr

 

[orthofish]

Are you using the small scoop end to dispense the powder, or are you using the flat-handled end?

Ann, I think I'm the only one on this entire forum that has done that :lol:

 

[Richard320]

It happened to me, too!

I added liquid Chlorine 2 evenings ago, enough to raise it to 17.

I was expecting to see 14 or 15 this morning. I got 18!!

Hmmmm. Never had that happen before, but it is fresh Chlorine, just bought about 3 days before. I'm thinking, "Maybe they under-rate the Chlorine to allow for deterioration?" I do the TA test, and instead of that red color, I end up with sort of a pale salmon color, so I'm guessing the Chlorine is, in fact, really high.

The Chlorine sample is still sitting there. I dribble a little extra water in it, get a pink cloud. Swirl. It disappears. Curious... Add some more. Same thing. Now I'm wondering. So I dump, rinse, and repeat the test, but this time I swirl a long, long time. Now I get 17.

I'm thinking I have been getting complacent and not mixing things well enough to allow things to react fully. That, and the fact that I'm inexact when measure the Chlorine; I just guesstimate by the level on the side of the jug. I could be off by a cup either way.

 

[frustratedpoolmom]

Are you using the small scoop end to dispense the powder, or are you using the flat-handled end?

Ann, I think I'm the only one on this entire forum that has done that :lol:

No you're not... :lol:

 

[PaulR]

Re: It happened to me, too!

I'm thinking I have been getting complacent and not mixing things well enough to allow things to react fully.

The FAS-DPD drops react pretty quickly but I think you still want to allow a second or two between drops. I've noticed even with the speed-stir the TA test takes a second or so to fully mix. putting in drops as fast as you can count might be overdoing it...
--paulr