Figuring out pool gallons, Irregular pool shape

Chemingway4

Member
Apr 23, 2019
15
Bakersfield California
Hello. Lately I’ve been thinking I might be calculating our pool size incorrectly. It’s an odd shape as you can see. Any ideas of what you think it is? I’ve been using 26,000 gallons since we bought the house, but I don’t remember how I got that number. 😂

Shallow end is 4 feet
Deep-end is 8 feet.
The longest length is about 35 feet
Deep-end width is 16 feet

Thank you!
Carolyn
 

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RMcGirr83

Gold Supporter
Nov 19, 2018
112
Tuscola, TX
I think you need some more measurements. length is fine, but I would measure three widths. Shallow end, middle, deep end. Then I guess average them as well as average the depth. Just using your numbers and averaging the depth I'm coming to ~17k gallons (35x16x4x7.5) ish.
 
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AUSpool

Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
571
Brisbane, Australia.
Well hay there, 1st post, welcome to the forum, you’ve come to the right place for all your pool questions.

I would break it down into smaller pieces then add them up. From the first image cut off a half circle. Calculate a circle with average depth and divide by 2. Then come down the pool to create a rectangle, then a triangle and finally a rectangle all at average depth for each shape. Then add the ‘hip’ to the middle left with another half circle + rectangle.
 
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PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
2,947
Damascus, MD
Mine is a similar shape but when I first filled it, I took water meter readings before and after. If you ever empty it, use your water meter or get a high quality inline hose meter. You can also get a pretty accurate volume measure by adding specific amounts of chemicals and noting the before and after test of that chemical. First step for that is to get a high quality test kit like the TF-100 (above).
 
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Chemingway4

Member
Apr 23, 2019
15
Bakersfield California
Mine is a similar shape but when I first filled it, I took water meter readings before and after. If you ever empty it, use your water meter or get a high quality inline hose meter. You can also get a pretty accurate volume measure by adding specific amounts of chemicals and noting the before and after test of that chemical. First step for that is to get a high quality test kit like the TF-100 (above).
I wish I would have thought to check the meter before/after because we just refill it a few weeks ago. 🤦🏻‍♀️ The reason I was questioning my calculation is because my chemical math isn’t adding up, so I think that might be the route I need to go. I’ve been trying to get the chlorine level right and the amount I’m adding isn’t getting me to the target level on the TFPC. It has me thinking my pool is more like 30,000+ gallons than 26,0000. So for example I’m using the Taylor 2006 kit. Yesterday morning I had a FC reading of 4.3 and wanted to raise it to 7.5. I added the amount suggested in cal-hypo (my CH is low so I thought that best) I waited until the evening to add it and a couple hours later retested and it was only at 6. That’s what made me think I might be off in my measurement. I realized this morning that I probably had some chlorine burn off during the day, so I’m gonna try it again this evening. What do you think? Would monitoring the chlorine level help me figure out the correct gallons?
 

Chemingway4

Member
Apr 23, 2019
15
Bakersfield California
Well hay there, 1st post, welcome to the forum, you’ve come to the right place for all your pool questions.

I would break it down into smaller pieces then add them up. From the first image cut off a half circle. Calculate a circle with average depth and divide by 2. Then come down the pool to create a rectangle, then a triangle and finally a rectangle all at average depth for each shape. Then add the ‘hip’ to the middle left with another half circle + rectangle.
Thank you. I’m going to try to break it down like you suggested. 👍
 

jimmythegreek

Bronze Supporter
Aug 10, 2017
770
Morris Cnty NJ
I think you are pretty close with 26k gallons. Like said before if you measure in pieces with more detail like where the depth starts and ends before hopper we can get better numbers but I think you are close
 
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Chemingway4

Member
Apr 23, 2019
15
Bakersfield California
I think you need some more measurements. length is fine, but I would measure three widths. Shallow end, middle, deep end. Then I guess average them as well as average the depth. Just using your numbers and averaging the depth I'm coming to ~17k gallons (35x16x4x7.5) ish.
You’re right; I need more measurements. I know it’s more than 17k gallons because of the chemical amounts I have to use. I’m gonna keep working on it. Thank you!
 

Teald024

TFP Guide
Using the chemical additions is an easy way of determining the pool volume. Since you used cal-hypo, you have a double way to test the volume. One with the FC and another with CH. Since cal-hypo adds a known amount of FC and CH, you can test both, add a known weight of cal-hypo and then retest an hour later. In PoolMath, there is a tab/area for Effects of Adding Chemicals. Adjust the pool volume in PoolMath until it matches your resulting gain of FC and again for CH. You should get similar volumes for both. Use the new pool volume for your next additions and see how it compares with the expected results. Forget about all that crazy math, unless you like that sort of puzzle.
 
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Chemingway4

Member
Apr 23, 2019
15
Bakersfield California
Using the chemical additions is an easy way of determining the pool volume. Since you used cal-hypo, you have a double way to test the volume. One with the FC and another with CH. Since cal-hypo adds a known amount of FC and CH, you can test both, add a known weight of cal-hypo and then retest an hour later. In PoolMath, there is a tab/area for Effects of Adding Chemicals. Adjust the pool volume in PoolMath until it matches your resulting gain of FC and again for CH. You should get similar volumes for both. Use the new pool volume for your next additions and see how it compares with the expected results. Forget about all that crazy math, unless you like that sort of puzzle.
Thank you for replying. I actually have 3 ways of checking after thinking about it. We drained and refilled the pool a couple weeks ago and I added 10 lbs. of conditioner because it was at zero. I ran out of solution to recheck the CYA level so as soon as I get the new bottle (should arrive tomorrow) I can recheck and see where it's at. That's probably going to be my best bet because I know it was at zero to start with. So using that tab you told me about, the CYA should be about 46 (40-50?) if my pool really is 26k. Thank you for your help!!
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
2,947
Damascus, MD
Using CYA might not be the best of tests since the CYA test is hard to master. But it should get you in the ballpark! Especially good if you get a bottle of the reference 50 ppm solution.
 
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Poolmama!

Silver Supporter
Feb 20, 2019
22
Dallas, Tx
Not sure about your area, but here we can call the city water department and they can tell you by hour how much water you've used. Give them the day and times you were filling your pool and they might be able to tell you the gallons used. I guess it depends on what kind of meter (smart meter?) you have?
 
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Chemingway4

Member
Apr 23, 2019
15
Bakersfield California
Not sure about your area, but here we can call the city water department and they can tell you by hour how much water you've used. Give them the day and times you were filling your pool and they might be able to tell you the gallons used. I guess it depends on what kind of meter (smart meter?) you have?
Poolmama, good idea! I logged into my water account, but I can only see my usage for the month, not specific days. But, if I compare this months bill to the same month last year, I used 26,989 gallons more, so maybe my estimate of 26k is pretty close! :)
 
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