new salt chlorinator system

[chem geek]

A question though, in step #6, is "washing soda (sodium carbonate)" the same as the bicarb (sodium bicarbonate?) that I use to raise TA?

No, those are related, but different. Washing soda (sodium carbonate) is what is in most "pH Up" products and raises both pH and TA. Baking soda (sodium bicarbonate) mostly raises TA with little change in pH (it can rise some depending on your starting pH). You use the former to raise both pH and TA at the same time and the latter to raise mostly TA only.

As for the CuLator replacement frequency, it depends on whether it fills up removing metals. You wouldn't replace it every couple of weeks unless you had a lot of metals in the water, the bag absorbed them (usually, but not always, coloring the bag), and you measured a drop in metal concentration but was still not low enough. Whoever described replacing it every couple of weeks was probably trying to make money from selling it, but even the manufacturer doesn't say to do it that frequently.

In fact, have you had your water tested for metal ion concentration? Such tests usually measure total concentration including metals bound to sequestrants when the dye in the test binds more strongly to the metal than the sequenstrant you are using. Ben's bucket test would be a more definitive test since it eliminates the sequestrant by reacting with it to release the metal.

By the way, having the FC that is 5% of the CYA level didn't come from me exactly. There was a user at TFP making careful measurements that found precisely for his pool where chlorine demand would start to increase from algae growth and then we looked at other user's SWCG pools at varying phosphate levels (when they knew them) and at some point proposed setting the lower standard since it seemed that the SWCG pools were able to prevent algae growth at the lower FC/CYA level. My contribution was for the FC/CYA ratio being consistent across CYA levels and initially I proposed a 4.5% setting but that level was based on actual pool reports, not on theory. 5% is the rounded version of that which ended up in the recommendation tables as 3 ppm FC for 60 ppm CYA to 4 ppm FC for 80 ppm CYA. I also looked at the chemistry of the SWCG cell to figure out that there would indeed by super-chlorination of a portion of the water in the cell that was different than occurs from manual dosing (the difference being the pH, at least initially).

[PoolDoc]

You wouldn't replace it every couple of weeks unless you had a lot of metals in the water, the bag absorbed them (usually, but not always, coloring the bag), and you measured a drop in metal concentration but was still not low enough. Whoever described replacing it every couple of weeks was probably trying to make money from selling it, but even the manufacturer doesn't say to do that.

The mfg is saying every 30 days (4 weeks):

Discard used PowerPak after 30 days. (Note: PowerPak contents MAY change color.)

from
http://www.culator.com/eliminating-metals

[JimK]

No, those are related, but different. Washing soda (sodium carbonate) is what is in most "pH Up" products and raises both pH and TA. Baking soda (sodium bicarbonate) mostly raises TA with little change in pH (it can rise some depending on your starting pH). You use the former to raise both pH and TA at the same time and the latter to raise mostly TA only.

As for the CuLator replacement frequency, it depends on whether it fills up removing metals. You wouldn't replace it every couple of weeks unless you had a lot of metals in the water, the bag absorbed them (usually, but not always, coloring the bag), and you measured a drop in metal concentration but was still not low enough. Whoever described replacing it every couple of weeks was probably trying to make money from selling it, but even the manufacturer doesn't say to do it that frequently.

Thanks for the clarification.

In fact, have you had your water tested for metal ion concentration? Such tests usually measure total concentration including metals bound to sequestrants when the dye in the test binds more strongly to the metal than the sequenstrant you are using. Ben's bucket test would be a more definitive test since it eliminates the sequestrant by reacting with it to release the metal.

I have not had my water tested. I thought I understood that the sequestrant I'm using interferes with such tests. Is this incorrect? Is there a specific test kit that will give me accurate results even with the sequestrant? I plan on trying Ben's bucket test, but it would be nice to know the level of metals I'm dealing with.

By the way, having the FC that is 5% of the CYA level didn't come from me exactly. There was a user at TFP making careful measurements that found precisely for his pool where chlorine demand would start to increase from algae growth and then we looked at other user's SWCG pools at varying phosphate levels (when they knew them) and at some point proposed setting the lower standard since it seemed that the SWCG pools were able to prevent algae growth at the lower FC/CYA level. My contribution was for the FC/CYA ratio being consistent across CYA levels and initially I proposed a 4.5% setting but that level was based on actual pool reports, not on theory. 5% is the rounded version of that which ended up in the recommendation tables as 3 ppm FC for 60 ppm CYA to 4 ppm FC for 80 ppm CYA. I also looked at the chemistry of the SWCG cell to figure out that there would indeed by super-chlorination of a portion of the water in the cell that was different than occurs from manual dosing (the difference being the pH, at least initially).

Thanks for the explanation. That gives me confidence that I've been using appropriate FC levels.