# Thread: how to determine pool size (gallons) for chemistry?

1. ## how to determine pool size (gallons) for chemistry?

Hi folks,

The house I bought has an irregular shaped pool with a good size section of it only 6" or so deep? The pool is kidney shaped with a small spa off one corner.

I've seen instructions for estimating the number of gallons by using length, width and average depth, but I'm not sure how to apply that to my pool given that "beach" area.

Here's what I can measure:
width at the ends is 11' and 14'
width in the middle is 12'
length of the "beach" area is 5'
depth ranges from 39" to 62" except for the beach area which is 6"
hot tub 6' diameter circle with a seat 16" below the water line that is 16" front to back

I've attached a drawing with the measurements I could take. Would anybody be able to help me figure out how many gallons I should assume when trying to figure out pool chemistry?

Thanks very much for any help!
rjb

2. ## Re: how to determine pool size (gallons) for chemistry?

The normal approach is to start with a rough approximation, average out the width, length, and depth, and use a rectangular pool volume calculator to get a rough approximation. Then watch to see if your various chemical additions have the desired effect, or are consistently low or high, and adjust your rough estimate as needed over many different chemical additions. With this approach you can get a good working volume number, but it takes a pool season or so to zero in on it.

3. ## Re: how to determine pool size (gallons) for chemistry?

I would estimate this pool to be roughly 10k gallons. I used 30' x 12'x 4'.

Your pool is roughly 5' deep, then 4' deep, then 3' deep. So take the middle number. And its 11' wide, 12' wide, and 14' wide. Take the middle number again.

I figure the "beach" area will equal some of the "spa" area. So that's a good estimation. Pool math says 10,800 for a rectangular and 9,800 for an oval. I'm splitting the difference again and betting on 10k. IT might be closer to 9k because of the beach area. But if it were mine, i would use 10k as my starting point. Then test and figure out if you are adding too much or not enough bleach. If pool math says to add 40oz to raise 4FC and you add 40oz and it raises it 5FC, then you know you are shooting too high....And vice versa for too low. If you add 40 oz and it only raises 3FC, then you need to shoot higher. Make sense?

4. ## Re: how to determine pool size (gallons) for chemistry?

Pentair has a calculator on their website that should get you a ballpark number: http://www.pentairpool.com/support/c...c/poolcalc.htm

5. ## Re: how to determine pool size (gallons) for chemistry?

Now, with kris77's estimate use Jason's trick (I used it all last season to zero in on my volume). Use your TF-100 test kit (you do have one, don't you?) to get a good FC reading. Then add a specific amount of one of the chemicals (I like chlorine, adding one bottle of the 8.25% stuff). Wait 30 minutes to an hour with the pump running and then test FC again. Use Pool Math to work backwards to see what volume had the effect you detected.

Now, that is based on no outside things happening to the pool like lots of direct sun in AZ or a full blown algae bloom consuming your FC.

• The size of your pool in gallons (I know this would be a guess until you zero in)

• If your pool is an AG (above ground) or IG (in ground)
• If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
• The type of filter you have (sand, DE, cartridge) and, if you know, the brand and model of the filter.
• If you know, please tell us the brand and model of the pump, and mention if is it a two speed or variable speed pump.
• Date of pool build/install, particularly important if less then a year old.
• What kind/model of water test kit you are using
• Other significant accessories or options, such as a spa , SWG, or cleaner

6. ## Re: how to determine pool size (gallons) for chemistry?

thanks to everybody for all the help. I have added the suggested information to my signature. At the moment, there is a pool service taking care of the chemicals so I do not have a water test kit. I understand that will be needed if I start maintaining the pool myself.

thanks again!!!
rjb

7. ## Re: how to determine pool size (gallons) for chemistry?

Fire the pool boy and put that money towards a TF-100. You can do it better and cheaper than they will EVER do. Unless you are the 1 in 1,000,000 that has a very good pool service.

Plus, I think its actually fun to do and interesting. It only takes me literally 5 mins a day to test and add bleach. Somebody on here has a signature on their profile that says...."A pool is like a pet, you have to feed it everyday, even if you don't want to play with it." And that is a VERY good analogy of taking care of your own pool. It needs attention every day...And 95% of those days, you will be "feeding" it bleach to keep it happy and clear. So if your pool service is only coming out once a week, your "pet" is starving.

8. ## Re: how to determine pool size (gallons) for chemistry?

Originally Posted by kris77
Fire the pool boy and put that money towards a TF-100. You can do it better and cheaper than they will EVER do. Unless you are the 1 in 1,000,000 that has a very good pool service.
I second that!!

9. ## Re: how to determine pool size (gallons) for chemistry?

If your pool is visible in satellite photos you can use a tool at www.gpsvisualizer.com/draw to measure the area of a polygon. Then you just multiply by your average pool depth to get cubic feet. Finally, cubic feet x 7.48 = gallons.

10. ## Re: how to determine pool size (gallons) for chemistry?

Once you get an approximate volume the other thing to watch when you have a test kit is your before and after adding a chemical water values. If you are consistently overshooting where you aimed for or undershooting then adjust your gallons accordingly. Soon you'll have it dialed in.

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