Improvements to Pool Calculator

[JasonLion]

For the next few days I am beta testing some improvements to my Pool Calculator. You can access the beta test version at Pool Calculator.

The Pool Calculator now remembers it's configuration. Units, pool size, goals, etc are all saved between sessions.

It is now easier to work with spas and very small pools. Small numbers of oz are now shown to the nearest tenth of an oz and if you mouse over a volume it will now show teaspoons in the info bar when appropriate.

The amounts of chemicals recommended to change the PH now take the current PH and TA levels into account. The calculation is still approximate and doesn't take other factors that might affect the quantities required into account, but in general it is now far more accurate than it was before.

This is a beta test version, as such not everything may work correctly and amounts of chemicals or other calculations might be wrong. Because of that I am leaving the old version up at the normal URL for the next few days. When this version has gotten more testing I will replace the previous version with the new one at the normal URL.

I welcome any testing, feedback, questions, or comments you may have!

Thanks
Jason

 

[JCJR]

I have high CH (540) and I need to refill, my tap water has 120 CH. I did not see where I can find out how much my CH will drop if I drain x amout of water.

Is this something that can be added to the Calculator?

 

[cwstnsko]

Just an observation, if I put in a combination of 500 gallons and 12.5% bleach, it tells me to add 1 oz to go from 3 to 7 ppm. If I put in 12% it tells me 2.1 oz, if I put in 13% it tells me 1.9 oz. If I switch it to 5000 gallons and keep 12.5% it says 20 oz. The 1 oz. recommendation seems out of line with the others. I'm not sure why I stumbled upon that on my 1st try, but just FYI it seems a little odd.

 

[JasonLion]

Just an observation, if I put in a combination of 500 gallons and 12.5% bleach, it tells me to add 1 oz to go from 3 to 7 ppm. If I put in 12% it tells me 2.1 oz, if I put in 13% it tells me 1.9 oz. If I switch it to 5000 gallons and keep 12.5% it says 20 oz. The 1 oz. recommendation seems out of line with the others. I'm not sure why I stumbled upon that on my 1st try, but just FYI it seems a little odd.

Thanks! Fixed now.

It was rounding the part to the left of the decimal point down and the part to the right of the decimal point up. It now shows the correct answer of 2.0, instead of 1.0.

 

[JasonLion]

I have high CH (540) and I need to refill, my tap water has 120 CH. I did not see where I can find out how much my CH will drop if I drain x amout of water.

Good point. Right now it can tell you what to do if your fill water has no CH, but there is no way to figure it out if there is calcium in your fill water. It would also be nice to have the calculation run the other way, right now it shows % to replace, but it should also tell you what happens if your replace X%. I will add both of those to the wish list for a future version.

 

[chem geek]

And you can add an option for one-time partial drain/refill dilution, which is the sort of calculation described in the posts above, or a continuous dilution which is computed by the formulas below:

Dilution % = 100% * ( 1 - EXP(-(Volume % / 100%)) )
Volume % = -100% * LN(1 - (Dilution % / 100%))

So replacing 100% of the water volume through continuous dilution results in dilution of around 63% (more than half diluted) so equivalent to draining 63% of the water and refilling. I'm defining Dilution % such that 100% would be a complete dilution or drain/refill.

Richard

 

[Jason]

I was playing on the beta pool calc, I set my pool volume to 13000 gal. All other items set to 0, except PH:

Set the "Now PH" to 6.8 and Goal to 7.4. This gave me a recommendation of 16oz by volume of borax. When I set the Goal to 8.8, it gave me the same result. Possible bug?

JasonM

 

[JasonLion]

Set the "Now PH" to 6.8 and Goal to 7.4. This gave me a recommendation of 16oz by volume of borax. When I set the Goal to 8.8, it gave me the same result. Possible bug?

Well, yes and no. The answer is wrong obviously, but that is the behavior I expect. The issue is in the way I estimate quantities for large PH changes. PH changes are very non-linear and I have a much simplified model that makes mistakes for large PH changes in general and for changes that go from well below a PH of 8 to well above a PH of 8 in particular. The error is also compounded because I don't handle TA near zero very well either.

Still, the results are much closer than they are using the previous version, which gave 69 & 228, when more accurate numbers would actually be around 8 & 73. Modeling PH changes is very difficult. The new approximation is better, but it is still far from perfect.

 

[austinnichols101]

I ran a test with my CYA level of 55 against the Chemgeek Chlorine / CYA chart and the results didn't return what I expected.

Poolcalc
CYA 55
Normal 3-6
Shock 15
Mustard Algae Shock 24

(the previous non-beta calc gave 4,9,17,32 as the corresponding values)

Chemgeek CYA chart (approximate values based on average of 50 and 60)
Min FC 4.05
Target FC 6.25
Yel/Mstrd Min 8.25
Shock FC 21.75
Yel/Mstrd Shock 32.15

Chemgeek approximations
"Min FC" is 7.5% of the CYA level = 4.125
"Target FC" is 11.5% of the CYA level = 6.325
"Yel/Mstrd Min" is 15% of the CYA level = 8.25
"Shock FC" is 40% of the CYA level = 22
"Yel/MstrdShock" is 60% of the CYA level.

 

[JasonLion]

You probably forgot to tab to the next field or press the calculate button. The numbers don't update till you do one of those. The Suggested FC Level calculation is the same as it was before, 4, 9, 17, 32. The remaining differences from Chem Geeks numbers are intentional. I have a slightly different interpretation of shock levels based on a slightly different interpretation of Ben's Best Guess chart.

 

[JasonLion]

Thanks to everyone who had a chance to try out the beta version.

I have moved the new features (remembering settings across sessions, more precision for small values, and improved PH calculations) into the regular version, available as always from http://www.poolcalculator.com/.

 

[matj6876]

Jason

I've been using poolcalc since last summer. You mention above that you have made changes to the Ph caculation.

My numbers today for my 15000 gal pool are:
FC 8.0
CC <0.5
pH 8.0
CH 480
TA 80
CYA 60
B 50
Na 3800
Temp 60F

At this stage I would usually add muriatic acid to take the pH down to 7.6.
I'm constantly battling rising pH so this is nothing new.
I would expect to add between 24 & 32 oz, as directed by poolcalc.
Right now it is telling me to add 12oz. Under half what it used to say.
Could you offer any advice?

 

[JasonLion]

PH calculations are complex. The new approximation is still an approximation, better in many cases than the old one, but not in your situation. The old calculation depended only on the starting end ending PH. The new one takes into account the starting TA. However, borates, salt, CH, CYA, and temperature also factor into the true value.

Assuming B 50 means borates are at 50, using a more exact calculation with your numbers I get 23 oz to go from PH 8 to PH 7.6. The borates make a large difference, as does the temperature. If your borates were zero it would be 9 oz. If the water was 90 degrees it could be more than double those amounts.

Because PH changes depend on so many different factors it is commonly impractical to calculate an exact amount. The Pool Calculator can provide a good starting point but you will always need to test after any addition and adjust as needed. With experience you get a feel for how your particular pool responds and can make better approximations.

 

[chem geek]

If you're a masochist, you can use the Pool Equations spreadsheet I wrote for more precise calculations, but it is not designed for novices. It looks like I really should spend some time creating a simplified model Jason can use for his online calculator, but I just don't have that sort of time right now (it's complicated to do).

Richard

 

[matj6876]

Jason - Thanks makes sense. Yes B 50 was my way of saying 50ppm of Borates, did not know what the correct abbreviation was. Before I saw your post I added 24 oz of acid and retested. pH went down to 7.6 so you are spot on with your math there as far as I am concerned! :-D

Richard - Wow! Just downloaded the sheet. That's going to have to wait til I get back from the next business trip but I'm up for a bit of masochism - looks like fun. Thanks!