SALT POOLS feedback please

[chem geek]

Sean,

As you know from other posts on this forum, many (but not all) SWG users experience rising pH which requires regular additions of acid to maintain pH (and possibly adding baking soda to maintain TA over a longer period of time). Non-SWG users using BBB or liquid chlorine do not generally see the pH rise unless they have high TA, low pH, aeration from water features, or a new plaster pool (that is curing). waterbear (Evan) has found that using 50 ppm Borates significantly reduced this acid demand, possibly by reducing chlorine demand and allowing for lower power levels or run times of SWG generation. We never definitively determined the cause of this pH rise but I believe it due to the hydrogen gas bubbles causing aeration to outgas carbon dioxide (the other primary candidate is outgassing of undissolved chlorine gas bubbles, but I find that less likely). Users who have tried running at lower TA levels (and avoided lower starting pH) have had less acid demand as well which is consistent with the carbon dioxide outgassing theory. I suggest that SWG manufacturers experiment with different approaches to managing the hydrogen gas bubble production, possibly segmenting or otherwise capturing the flow of hydrogen bubbles through the outlets so that they have less contact time with pool water or varying bubble size (if possible) since larger bubbles should be less effective at pulling carbon dioxide out of the water.

The issue that dawndenise has raised is valid in that normally SWG systems do not experience algae, but when they do you need to shock with a heck of a lot of chlorine due to the high CYA (70-80 ppm) recommended by most SWG manufacturers. Though the superchlorination effect in part of the volume of water through the cell seems to keep algae at bay for most users, it isn't perfect and the high CYA and typical recommended FC level (3 ppm) from the SWG manufacturer means a disinfecting chlorine level that is sufficient for sanitation, but not ideal for algae prevention if for some reason algae takes hold on pool surfaces and does not circulate through the cell. I would like to see the SWG manufacturers consider using larger (longer) plate areas (probably in longer cells) so that the power per unit area can be cut down which should allow for lower CYA levels to be used. A doubling of plate area (and a lowering of voltage to keep the total current the same or a reduction in "on" time to keep the total FC production rate the same) should allow the cell to operate efficiently at 35-40 ppm CYA instead of 70-80 ppm CYA.

That's my two cents worth. I don't own an SWG system (yet) so can only comment on what others have said.

Richard