Understanding the differences b/t the TFPC method and SWG manual

[Crunchy]

Not questioning it per se and I am heading down the TFP route, but I would like to understand it....below a table of TFPC targets and targets specified by my SWG user manual.

	Salt	CYA	FC	TA	pH	CH
TFP Ideal	4200	70	5	70	7.5	350
SWG Manual ideal	4000	50	2	120	7.5	225

Main question is why the much lower TA and higher CH using the TFPC method? if its too complicated or been discussed before then thats OK .

Thanks
Crunchy

 

[aussieta]

with a swg your ph will rise quickly
lowering ta will reduce the amount of ph rise and how much/often you need to add acid
to offset the drop in saturation index you raise your ch to compensate
with the salt level use your swg recomendation
tfp uses an average to suit all the different brands of swg

 

[Jezza]

Aussieta has covered the main points well.
Different manufacturers of SWG's have their own recommended salt level requirements and these should be what you follow. Remember that TA is about stabilising your pH to a point where ideally you don't need to keep adding MA as much to control the tendency of the SWG to pH rise- so this is what ultimately should be your goal.
Also keep in mind that you are also trying to keep your CSI around '0' to avoid either calcium scaling or pitting of your concrete pool. The manufacturers tend to disregard the importance of the FC/CYA relationship and therefore suggest lower levels of FC to be maintained.

 

[JoyfulNoise]

Just remember, gents, that the conditions INSIDE the SWG cell are nothing like those of the bulk pool water (this is where the manufacturers confuse things). One of the electrodes in the cell is generating large quantities of hydrogen gas. That generation plus the excessive aeration inside the cell can easily lead to the pH inside the cell being near 10 or higher. At that pH, the driving force for scaling is huge. So, by keeping the TA lower, you can starve the cell of some of the carbonate it needs to create calcite scale. At the very least, the lower bicarbonate alkalinity will reduce the pH rise in the cell from CO2 outgassing.

This is also why TFP considers adding borates to salt pools a major benefit. The borates will act as a pH buffer and effectively cut the pH rise inside the cell by nearly half. This has a huge effect on the potential scaling that can occur.

 

[Divin Dave]

Hi Crunchy,
The difference in the TA and the CH has to do with the Calcite Saturation Index (CSI). CSI is a measure of water balance. If its too high, it can indicate you are at risk calcium scaling, and if its too low, it can indicate you are at risk of the plaster slowly dissolving away.

TA buffers pH rise. If the pH rises too quickly and you have to add a lot of Muriatic Acid to bring it back down, then you can lower the TA to help out with that rapid rise and not have to add acid as often. Many of us have our TA all the way down to even 50 to control pH rise.

However, with the lower TA, you need to raise the CH a little bit to keep the CSI within limits. The science behind the CSI gets very involved and frankly, few of us understand it in large detail, but there are some here that do. You can probably read more about the science by searching "calculating CSI" or something to that effect. There is a search box at the top right of the page under the Pool School button.

Just below the Temperature row in Pool Math, is the CSI calculator. You can play around with it and see how changing your water parameters effects the CSI.

The TFP recommendation for FC, is to prevent algae as well as kill pathogens. Chlorine will kill agae and prevent it from reocurring if at the correct level.
If you keep your FC at 7.5% minimum to 11% of the cya level, that will prevent algae.

The Pool industry recommendation of 2, is for sanitation only, and then use algaecide and phosphate remover to control algae. The reason they do that is so they can sell more stuff for lots of money. The problem tough, is that it is expensive to go that route and honestly, it isnt nearly as effective as keeping your FC/CYA ratio per TFP recommendation.
Here is the science behind the FC/CYA ratio that we use. Pool Water Chemistry

The CYA recommendation of 70 is to lessen burn off of FC by UV from the sun. Doing so protects your FC a little longer and doesnt require you to run your SWG and pump quite as long, or at a higher ouput of the SWG. So, ultimately, this saves wear and tear on your equipment, saves on electricty and squeezes a little more life out of the SWG cell.

TFP does not recommend a salt level of 4200. I dont know where might have gotten that information. We recommend whatever the equipment manufacturer recommendation for salt level is. For SWG systems here in the US, that is usually somewhere from 3000 - 3400 ish, but there are some that recommend a higher salt level. Here is a link in TFP Pool School about swg levels. When in doubt, the information contained in Pool School always takes precedence as the official TFP recommendation.
Pool School - Water Balance for SWGs

I hope this helps a little.

 

[Crunchy]

Awsome - thank you people, makes sense, particualry given my current issues of calcium flakes and high acid demand - stay the course!

 

[Crunchy]

Thank you Dave for the very detailed response, it is all starting to fall into place :idea:, you guys must get tired of repeating the same thing over and over to us newbies but "We" do appreciate all the help and guidence from you all!

PS The TFPC salt level simply manufacturers rec + 200ppm.

 

[duraleigh]

PS The TFPC salt level simply manufacturers rec + 200ppm.

Where are you finding that? I cannot recall TFPC ever suggesting salt levels but you must have seen it somewhere.

 

[Sparkle]

Where are you finding that? I cannot recall TFPC ever suggesting salt levels but you must have seen it somewhere.

Water Balance for SWGs suggests "Salt 200-400 ppm ABOVE recommended optimum level"

 

[duraleigh]

Thanks. I have overlooked that. The "hard" number of 4200 was bothering me but I see that it is variable depending on your manufacturers suggestion

 

[JoyfulNoise]

Perhaps that "suggestion" needs to be revisited and modified.

The rationale for adding salt "200-400ppm above the manufacturers level" is that SWG's will typically run without problems if the salt level is on the high side (the electronics control/limit the current into the cell). Even my Pentair unit, with a HIGH SALT error code, will still generate chlorine. Conversely, SWG's don't typically run well when the salt is low and will often stop generating chlorine in order to protect the coating on the plates.

One reasonable situation where you would not want to start off higher than the manufacturers limit (and maybe even start a little lower) is in locations such as mine where you have low rainfall and high evaporation rates (desert type climates). In these areas, the "salinity" of the water will naturally climb over time with evaporation and refill. Most municipal water supplies deliver water that has some chloride in it and so, for desert climates, there is often very little need to add salt on a regular basis (I have never added any salt to my pool in years).

In more humid climates or those areas with winter rains and generally high rainfalls, you can reasonable expect to get significant wash-out of the pool water and have to add salt (chloride) on a regular basis. In those areas, starting off high is not a problem and probably a good idea.