Taylor Watergram Or Pool Calculator

[gutsrus]

If I put CH 400 and TA 100 with PH 7.4 at 78 degrees temp, the Taylor Watergram from my test kit shows a CSI of +0.1, while the Pool Calculator shows +0.86 for the same numbers. Taylor says it's balanced while PC says "Danger, Will Robinson". One of these appears to be FUBAR.

Any light?

[chem geek]

If I put CH 400 and TA 100 with PH 7.4 at 78 degrees temp, the Taylor Watergram from my test kit shows a CSI of +0.1, while the Pool Calculator shows +0.86 for the same numbers. Taylor says it's balanced while PC says "Danger, Will Robinson". One of these appears to be FUBAR.

Any light?

Check the "Units" in the upper-right which are probably set to Metric so the temperature is getting interpreted as Celsius (see if it says that in the temperature line). I can get +0.77 using your numbers with a CYA of 0 if I have the calculator set to metric with 78 Celsius. I'm not sure how you got +0.86 with your numbers.

If I use U.S. units, then with your numbers I get +0.06 which is close to the Taylor Watergram.

Richard

[gutsrus]

Check the "Units" in the upper-right which are probably set to Metric so the temperature is getting interpreted as Celsius (see if it says that in the temperature line).

Units were set to US. Might have been a glitch, the numbers seem closer now, but not enough to bank on.

I can get +0.77 using your numbers with a CYA of 0 if I have the calculator set to metric with 78 Celsius. I'm not sure how you got +0.86 with your numbers.

If I use U.S. units, then with your numbers I get +0.06 which is close to the Taylor Watergram.

Richard

All else being the same, (CH 460, TA 80, PH 7.4, WT 82) I now get -0.18 with the PoolCalc, and +0.1 with the Watergram. The WG only asks for those four factors, while the PoolCalc has more variables (like salt).

Since I'm still getting some "calcium dandruff" discharging from the SWG, I'm thinking I need to believe the Taylor WG, and use it a a guideline to run a slightly negative CSI until the stuff clears (with PH 7.2 PoolCalc says -0.37 and WG says -0.1), or until I can do a partial drain & refill to get the CH down....

[chem geek]

The Taylor watergram does not take into account Total Dissolved Solids (TDS) and assumes a typical non-salt pool at around 500 ppm. A saltwater chlorine generator (SWG) pool has around 3000 ppm salt which is 3200 ppm TDS. This lowers the CSI by about 0.2 so the Pool Calculator is more accurate for that. I would use The Pool Calculator rather than the Taylor Watergram, especially for an SWG pool.

Usually for an SWG pool you will want to target around -0.2 for the CSI because the salt cell has very high pH at one of its plates so in practice that means that targeting around 0 on the watergram will get you there. You can, of course, go lower, but then have the water be more aggressive to dissolving plaster. Most people can target -0.2 with the CSI and not get the kind of calcium deposits you are seeing, but note that there will always be some buildup, then cell reversal, then dispersal as that's what the SWG cells do. There isn't a way completely around it without making the water too aggressive.

One thing you can do that is very helpful in SWG pools is to add 50 ppm Borates to the water (either through a combination of 20 Mule Team Borax and Muriatic Acid, added alternately and separately, or by adding Boric Acid). This acts as an additional pH buffer, especially against a rise in pH, and will reduce the amount of pH rise at the plate that generates hydrogen gas, thus reducing the amount of scale that is built up at that plate. The Borates are also a mild algaecide so can lower the chlorine demand letting you reduce the SWG on-time and this will reduce the rate of pH rise in the pool overall. Products such as ProTeam Supreme Plus are pH neutral and mostly boric acid. ProTeam Supreme is essentially the same as 20 Mule Team Borax (except for hydrated water content) but will require acid addition.

Richard