Some questions about Pool Calculator

[pakrh8r]

I have been using the pool calculator for a couple months now and have some questions. I am curious as to why the volume seems to be higher than when I calculate it myself using the following formula: L x W x D x 5.9 (5.9 is the multiplier for oval pools that I have seen on a vast majority of sites). My calcuations come to 12' x 18' x 4' x 5.9 = 5,097.6 whereas the pool calculator equates it as 5500 gallons. What is the formula that the calculator uses and which is more accurate? Will 400 gallons make any difference in accurately testing and adding chemicals? I also have a question about the goals and target numbers. Reading the info on the calculator and a few of the earlier responses, it seems that the target level is the minimum level that I should have for the particular level I am testing for, correct? If so, then why does the goal have a bottom number lower than the target number? Should I strive to have the levels at a number in the middle of the goal? Also, the TA goal on the calculator for my pool is 70 - 90+ using the TFP choice in the dropdown at the bottom. What's with the plus? Does that mean I can have it higher or should I keep it at about 80? My prior Taylor test kit and I think my pool and/or heater manual suggest 80 - 120. Thanks.

 

[JasonLion]

There are two definitions of an oval, the mathematical definition, and the pool definition. A mathematical oval is like a circle that has been stretched, while a pool oval is a rectangle with half round end caps. If you use the mathematical definition of an oval you get the volume that those other calculators are giving you.

In any case, 400 gallons won't make a significant difference.

Most goals are expressed as a range, keep the level between A and B. Most numbers will drift in some consistent direction. In that situation, when the level gets to one end of the range you should adjust it to the other end of the range. Trying to maintain a level at some exact spot is very difficult and a waste of time and chemicals, thus a range rather than a single target number.

However, for chlorine there is a minimum and a target. Minimum is the number you should never go below. Target is a guess at what your need to raise FC up to to insure that it is at least the minimum 24 hours later. However for FC you have to figure out what an appropriate target level really is for your pool in particular.

The + on some TA ranges means that having TA higher than that may or may not be a problem depending on other factors.

 

[pakrh8r]

Thanks JasonLion. Great job on the calculator by the way and thanks so much for making it available to all of us. I'm still confused about the difference between volume mathematically and for a pool. Even if I break my 12' x 18' x 4' deep pool into the circle and rectangle (12' circle & 12' x 6' rectangle) and add up the 2 volumes, I still get the same result. Why would a pool volume be any different that any other volume? Isn't volume volume? Make sense what I'm getting at? If not is there a different multipier that I should be using? I know that even after you said the 400 gallons wouldn't make any difference I may be nitpicking, but I want to make sure I understand the concept. Thanks.

 

[JasonLion]

The problem is that there are two different shapes that are both called an "oval". These are different shapes with different volumes. If your pool has two straight sides and half round ends at either end, then it is the kind of oval that the Pool Calculator is using in it's calculations. If your pool is a "true" oval, the edge is curved all the way around with no straight lines anywhere, you want to use the equation you gave originally.

For a pool oval, two straight sides, you have a 12' circle and a 6x12 foot rectangle. Surface area is (6*6*3.14159)+(6*12) = 185 sqft. Depth of 4 feet is a volume of 740 cubic feet. There are 7.48 gallons in a cubic foot, so volume in gallons is 740*7.48 = 5535 gallons (give or take).

 

[pakrh8r]

That makes sense. I think by breaking it down into a square and rectangle I basically had it correct, but the mutiplier was off. If I had used the 7.48 for the gal per cu ft instead of the 5.9 multiplier I used it would be correct. Doing it that way I use pi * r squared * 4 * 7.48 = 3,382.15 where r = 6, adding that to the rectangle of 12 * 6 * 4 * 7.48 = 2,154.24. Totaling those two I get 5,536.39 gallons. I know that is a little different than how you did it but I believe it is still correct. I'l feel more confidant now that i have a good number to use. Thanks alot, I appreciate it.