Role of 12% bleach in preventing WS in the Liquidator?

[Water_man]

Last year chem geek gave a detailed analysis of the chemistry of the bleach solution on top of the Liquidator. This solution is enriched with chlorine more than the pool water, although its concentration there is a lot lower than that of the bleach at the bottom. Also, the pH there is supposedly higher than that of the pool water.

The analysis predicted that adding borates may eliminate WS (insoluble Calcium salt) settling on the Liquidator tubing and flow indicator. This is indeed what happened in my pool system, when I added borates this year. However, borates was not the only parameter that was changed this season. I also changed this year to 12% bleach as compared to 6% last year, when I had WS. Someone indicated recently that 12% bleach may help to eliminate the WS. I wonder if this is true, and if it is, what may be the mechanism? Don’t we expect higher pH at the top solution for 12% bleach as compared to 6%?

 

[chem geek]

Yes, I would expect that the concentration of chlorine would be somewhat higher and the pH would be a little higher as well. This is not only because the chlorine is twice as concentrated, but also if the water above is more concentrated with chlorine, then the flow rate will be a little lower. However, this affect probably doesn't scale linearly, at least not with pH as I calculate below.

If I assume a 1000:1 dilution of the water on top relative to that below, then assuming a TA of 100 ppm, CYA of 30 ppm and no Borates, the pH using 6% bleach would rise from 7.5 to 8.8 with an FC of 62 ppm and a saturation index of +1.26 . If instead I use 12.5% chlorinating liquid in the calculation, the pH rises to 9.0 with an FC of 125 ppm and a saturation index of +1.41. If I use 50 ppm Borates, then with bleach the pH rises to 8.1 with a saturation index of +0.64 while with chlorinating liquid the pH rises to 8.3 with a saturation index of +0.78.

So the bottom line is that the Borates play a much greater role in keeping the saturation index lower than the use of bleach vs. chlorinating liquid and in theory the chlorinating liquid should be worse, not better, in terms of scaling issues, but the difference isn't huge. I also assumed the same dilution ratio for bleach and chlorinating liquid -- I really don't know how the rates of diffusion are affected precisely. In theory, it should be concentration dependent so one might expect chlorinating liquid to be even worse than described above, but there are other factors including differential density of the two (chlorinating liquid is denser than bleach).

Richard

 

[Water_man]

Assuming the level of borates is the same (50 ppm) I don't follow how 12% bleach may be better than 6% bleach for the purpose of reducing scaling, other than a lower flow rate with the 12%. Is this is what you meant?

 

[chem geek]

Yes, the chlorinating liquid would theoretically be worse, not better, than bleach as far as scaling was concerned. Of course, what goes on in The Liquidator is complex so really one would have to get to a steady-state with each and measure the actual chlorine level and pH in the upper layer to get an idea of what's really going on.

 

[heatmisr]

I have used the Liquidator for 2 seasons with the 12%. I originally started with 6%, but had to switch to 12% because of the flow issues. I got the WS last year with the 1/2" tubing, but it didn't change the flow pattern at all. The highest flow I could get was 3 (it was a struggle to get that) and I had to partially close the skimmer valve and have the valve to the flow meter wide open to get any flow at all.

I switched over this year to the 3/8" tubing and the flow is much improved. However, the WS developed much faster and I think it is worse. Since the flow is better, I needed to turn it down. I can now get a flow of 3 with the skimmer valve wide open and the flow meter valve partially closed. This is too much though. I run through 4 gallons of 12% in about 2-2 1/2 days, which I know is too fast. My pump is on a timer. I run it for 6hrs twice a day. When I turn the flow down to get to a flow of 1, I start developing flow problems. It flows fine until the pump turns off and has to come back on. The flow is not strong enough to "blast through" the WS, so I get no flow at all. I never considered it might be because of the density of the 12%.

Since it is late in the season, I decided to finish it out with the 12%, but next year, I plan to run with the 6% and see if that makes a difference with the white stuff and the flow issues. I suspect that it will.

ETA: Bottom line is I believe the 12% makes the WS worse, not better.

 

[Water_man]

ETA: Bottom line is I believe the 12% makes the WS worse, not better.

Then try 50 ppm borates next year. It's good for the pool, body and soul, and most likely, possibly for the LQ.

 

[Bama Rambler]

I just changed just the suction line on my LQ and now can get a flow of 5+ with the skimmer line wide open. I left the fill line 1/4". I also bought 3/8" NPT check valves instead of the 1/4" so hopefully the WS won't be an issue.

 

[heatmisr]

ETA: Bottom line is I believe the 12% makes the WS worse, not better.

Then try 50 ppm borates next year. It's good for the pool, body and soul, and most likely, possibly for the LQ.

I considered it. I will try the 6% first to see if it makes a difference. If not, I'll go with the borates.

 

[Water_man]

Yes, the chlorinating liquid would theoretically be worse, not better, than bleach as far as scaling was concerned.

Too bad we don't have enough empirical data to support the theory. Maybe next season I'll start with 6% bleach (and 50 ppm borates) and see what happens for a couple of weeks. In case the theory is right, the positive effect of borates is so remarkable, that at least in my case, 50 ppm borates more than compensated for the increase in bleach strength from 6% to 12%.