Posted by Kirk Gilmore on February 3, 2010 at 9:00am
Chemicals present in the pool water can breakdown when exposed to the harsh climate inside the generator cell. At some point inside a cell the chlorine can reach 50ppm and most chemicals (Algaecide, Scale Inhibitor) can only withstand about 10ppm.Example: Phosphorous based HEDP, or phosphonic acid, works pretty well as a anti scaling or sequestering agent for traditional pools or spas, but in a salt pool with the extreme conditions of the cell this products tends to break down into orophosphate, which is a fertilizer. Once the chlorine drops in a salt pool you can start to grow algae. Orophosphates also is one of the fastest growing types of scale that tends to layer right on the cell and shortens its life.Does anyone know of any chemical company that is trying to address this problem with a new line of chlorine generation chemicals that can withstand the enviroment inside the cell?
Ross makes a very good point since typical saltwater chlorine generators (SWGs) in a residential pool situation do not output particularly high chlorine levels out of the returns and therefore the average chlorine level in the cell must be the same as well. However, near the chlorine generation plate, the chlorine level can be very high and the pH is also low which means that CYA won't moderate chlorine's effectiveness as much. The active chlorine (hypochlorous acid) level is quite high (some manufacturers claim around 50 ppm FC between the plates), though obviously exposed to a fraction of the total water volume through the cell. So there is no doubt more oxidation occurring in that water fraction but it will take many turnovers of water to get most of it exposed to this higher chlorine level and such exposure will be relatively brief (seconds).
As for prevention of scaling, first and foremost one can target a slightly negative saturation index, but not too much -- say, -0.1 to -0.2 -- using The Pool Calculator which has a more accurate calculation, especially at higher TDS (saltwater chlorine generator pools) and higher temperatures (spas). In addition, one can use 50 ppm Borates in the pool since that is an additional pH buffer that significantly cuts down the rise in pH at the hydrogen gas generation plate. Finally, one should use an SWG system that periodically reverses polarity of the plates as this significantly reduces the rate of sustained scale buildup over time.
Kirk,
You could well be right adjacent to the anode,but not in the whole cell. The average chlorinator system,say around 25 grams would be lucky to have 2ppm coming out of the returns. large bypass systems of say 750 amps on commercial pools have 50ppm exiting the cells.
Maybe you could look at an electrolysis system that does not need scale inhibitors or phosphate removers like the system at www.magnapool.com
We have used phosphonic acid a few times for this problem and have not experienced any negative effects. The application was 1 quart of Salt Boost by AquaChem per 15,000 gallons. I would think that a properly sized chlorine generator working with a typical flow rate would keep the concentration of Cl in the cell down to an acceptable level.
Macgreyel products. Beautec, Scaletec....works fantastic! I have taken nasty scale rings off tile with it. not super quick, after a few applications. I did 1 gallon of scaletec for 2 months, then maintenace doses of beautec there after. If the scale on the tile is thick, use the bio-dex 300 tile cleaner, a acid wash brush and some elbow grease to get it gone. then do the scaletec and beautec to remove from the surface.
Comments
As for prevention of scaling, first and foremost one can target a slightly negative saturation index, but not too much -- say, -0.1 to -0.2 -- using The Pool Calculator which has a more accurate calculation, especially at higher TDS (saltwater chlorine generator pools) and higher temperatures (spas). In addition, one can use 50 ppm Borates in the pool since that is an additional pH buffer that significantly cuts down the rise in pH at the hydrogen gas generation plate. Finally, one should use an SWG system that periodically reverses polarity of the plates as this significantly reduces the rate of sustained scale buildup over time.
You could well be right adjacent to the anode,but not in the whole cell. The average chlorinator system,say around 25 grams would be lucky to have 2ppm coming out of the returns. large bypass systems of say 750 amps on commercial pools have 50ppm exiting the cells.
Maybe you could look at an electrolysis system that does not need scale inhibitors or phosphate removers like the system at www.magnapool.com