Trying to determine pool size

[Tito_cen]

Hey guys it's been a while since I have been on here! I just purchased a new home and I have a pool I am trying to determine size for proper chemical dosing! Here is a diagram I made with measurements and depth, its kind of too much for me to handle I think . I have been researching and am considering doing the TA test to chemically determine size. Not trying to get anyone to do the work for me, just point me in the right direction. Any help is greatly appreciated! I calculated roughly 30,000 gallons. (Prev owner said 40,000 pool store says 24,000)

The pool is a free form pool and measures 48.5 feet long and has different widths (18'6", 13'6" 12'8") as seen in diagram. Depths go from 2ft (sun ledge) to 6'4" (center). The spa is 8 feet 10 inches in diameter, but has a 16" bench all the way around!


TIA

Hector

 

[zea3]

If you have a test kit, test your FC and use PoolMath to calculate how much chlorine to add to reach 10ppm, using your 30k estimate. Let the water circulate 15 minutes and test again and see how close you were to the target. If you went too high, the pool is smaller, if you didn't add enough then the pool is larger.

 

[Tito_cen]

If you have a test kit, test your FC and use PoolMath to calculate how much chlorine to add to reach 10ppm, using your 30k estimate. Let the water circulate 15 minutes and test again and see how close you were to the target. If you went too high, the pool is smaller, if you didn't add enough then the pool is larger.

Awesome! I do have the TF-Pro! I will try that later today or tomorrow.

So to confirm just wait 15 mins? No need to wait hours? I normally add liquid chlorine in front of return jet, should I disperse it all along pool? Thanks!!

 

[zea3]

To see if you hit your target you only need to wait long enough for it to mix in. It is best to add it in front of a return jet. If you wait hours then organics or uv exposure can consume some of your FC and you won't get a true picture of how much it raised the FC. This is just for checking if you estimated the size of the pool correctly.

 

[drsipe]

My pool builder's documentation stated my pool was 24500 gal. This year I converted to SWG, so I had to bring the salt level up. I added the salt in three steps. The first 240 lb raised the salt level by 1000 ppm. The second 240 lb addition also raised the salt level 1000 ppm. Playing with pool math, adding 240 lb of salt raises the salt level by 1000 ppm if the volume of the pool is 28700 gal. I've had the pool since 2004, and I've been using the wrong volume to calculate chemical additions for 17 years.

 

[IceShadow]

Here’s the way to use TA. Will get you within 100gal or so with pretty good accuracy.

A Chemical Way of Calculating Pool Volume

There is a way to use pool water chemistry to calculate pool water volume without using the traditional geometric calculations. The geometric formulas are fine for pools that are traditionally shaped. However, when pools do not fall into these convenient shapes, a chemical method can be used...

www.troublefreepool.com

 

[EmilyOTR]

I have the same issue, I don't know my pool's volume. What is interesting, is I used pool math (inputting 12,000 gallons) to put in salt and it told me 6 bags plus 1 lb (241 lbs) would bring me from 1,000 to 3,400. I put 6 bags in and I'm at 2200! Now, it hasn't quite been 24 hours, should I wait longer or can someone tell me what my volume is?

 

[EmilyOTR]

Holy Crud I just did what drsipe did, and based on going from 1000 to 2200 with 240 lbs of salt means my pool is 24,000 gallons. could I be that off or is a very inaccurate way to do volume?

 

[zea3]

I don't know if the salt is an accurate measure to determine pool size. I would determine size based on the FC test I described or the TA method in the article linked in IceShadow's post.

 

[drsipe]

I don't know if the salt is an accurate measure to determine pool size. I would determine size based on the FC test I described or the TA method in the article linked in IceShadow's post.

I agree that the salt test is not the most accurate (I believe it is + or - to 200 ppm). For me it did start the wheels turning and I discovered that my pool has a higher volume than the builder stated. If I use the "old pool math", it calculates out to about 29000 gallons. My pool is a true L, with a diving end, so calculating the diving well is where any miscalculation will occur. Between the "old pool math" and and the salt testing, I think I'm probably closer to 28700 gal than the 24000 stated by the builder.

 

[EmilyOTR]

the TA method seems like it would really throw off pH, or am I not understanding? I will have to get a measuring cup to do the FC method, since I don't generally measure.

 

[IceShadow]

Baking soda moves up TA but doesn’t increase pH too much. The higher TA will cause the pH to creep up over time but acid will lower both.

What is your current TA?

 

[IceShadow]

Per pool math, 5lb of baking soda is expected to raise the TA by 24 in a 15k gal pool.

 

[EmilyOTR]

my TA is 90. I don't think I want it higher as I want to add acid less.

 

[IceShadow]

You could wait until your pH is high, then do this:


If the Total Alkalinity of the pool is high (over 160 ppm) and you want to lower the TA instead of raising it, then you can use muriatic acid (31.45%) to lower the alkalinity to determine the pool volume. The formula for adding acid is as follows:

125,000 (formula number for Muriatic Acid) times (X) the quarts of acid added, divided by the ppm reduction in alkalinity. Of course, be careful to not add too much acid at one time. Generally, it is safe to add two quarts of acid per 20,000 gallons of pool water when the TA is over 160 ppm, and the pH is above 7.7. Two quarts of acid will lower the TA by 12.5 ppm per 20,000 gallons.

 

[EmilyOTR]

I'm not clear on that. I add however many quarts I want? So I could add one quart then I'd multiply by 125,000, which is 125,000 and divide by how much my alkalinity goes down? I didn't think one pour of acid could lower TA that much.

 

[IceShadow]

That is correct. Keep in mind you are testing with 10x the pool water and the reagents and each drop is 1 TA to give you precision within 1 TA. So you can measure and if the TA goes down by 8 with one quart of acid you can know your pool is in the neighborhood of 15k gallons.

Two quarts would double your precision.

 

[EmilyOTR]

maybe after this week when the weather really cools down, 2 quarts would probably make my pH pretty low. 10 x the testing water? what do i test in? That's a lot? and a lot of manual swirling!

 

[Tito_cen]

Thanks for all the replies! Will try both FC & TA methods!

Can I get by without a tablet floater? I test often and use liquid chlorine. The reason being is I have really strong winds here so my floater always goes to same corner and stains that area, and no where to tether to. I tried the "sunken treasure" sinking chlorinator and it stained my plaster even though company assured it would not

 

[IceShadow]

maybe after this week when the weather really cools down, 2 quarts would probably make my pH pretty low. 10 x the testing water? what do i test in? That's a lot? and a lot of manual swirling!

Since it’s 250ml, it’s around a cup. I did it in a 2-cup measuring cup. Stirred with a bamboo skewer. Ended up with the same 20k gallon calculation that the geometric math told me.