Lowering Alkalinity

[PoolJunkie]

OK, so I made a huge miscalculation and added 4x the amount of pH-plus that I needed. I ended up with a pH greater than 8 and drove my Alk from a perfect 120 to 240! Curse me!!

Thank you so much for the tutorial on lowering pH. As a former chemistry major, it makes PERFECT sense to me. Thank God I do not work in a lab with my present-day lack of diligence with my calaulations!!

In bringing my pH back to 7.5 last evening with dry acid, the Alk already came down to 210. I then read your tutorial this AM and started running the deck jets to agitate the water surface. I have the pH down to between 6.8 and 7 now and will hold it there until the Alk gets to 120.

We are going out of town tomorrow for an overnight and will be back the next day. I feel like I should close the pool cover until we get back. I realize the process will stop during that time, but would you expect me to lose any ground? I am hoping to be done by then, but if not should I leave the pool uncovered? I HATE cleaning my filters and we occasionally get unpredicted dust storms here, so we usually never leave it open even to leave the house for a few hours.

[CarlD]

No sure what pH-Plus is. Is it Sodium Carbonate--soda ash? If it is, then Arm&Hammer Washing Soda is the same thing and probably 1/3 the price.

What lowers T/A is lowering the pH, not the aeration. The aeration RAISES pH but does it without raising T/A at the same time, unlike Sodium Carbonate or even Borax.

So you LOWER pH to bring T/A down with it (T/A moves with pH).
Then you aerate to RAISE pH again with increasing T/A.
Then you lower pH again, bring T/A down again.
Then aerate.

Keep doing this till your T/A is where you want it, then stop.

[Watermom]

Raise your pH just a little. Since 6.8 is the lowest value on the scale, it could mean 6.8 or it could mean anything lower than that. If you raise it to 6.9 or 7.0 you can be sure what it is instead of risking that it might actually be 6.4 or something and damaging your pool!

[PoolJunkie]

pH Plus is the HTH sodium carbonate product. I should have used about 60oz, actually used 240 . . . not one of my prouder moments.

If I understand correctly, the lower pH drives conversion of the bicarbonate/carbonate balance toward the formation of carbonic acid and free CO2 which decreases alkalinity. The CO2 must escape to the atmosphere for pH balance to be restored (pH goes up due to removal of carbonic acid which is breaking down to CO2 and leaving the solution as a gas). It is the removal of the CO2 which is facilitated by the aeration. It would seem that the better I maintain pH near 6.8 to 7.0 the faster CO2 will be formed and blow off with aeration.

Once I hit an alk of 120 and stop adding acid, I would assume I should keep aerating until the pH has come back up in order to avoid letting the alk go back up also?

[CarlD]

I would NEVER recommend letting your pH go below 7.0, let alone keeping it there. While in the lab 7.0 is "neutral", in the pool it is BELOW the optimal range of 7.2-7.8! I strongly recommend you use 7.0-7.2 as your range rather than 6.8-7.0.

If you have a vinyl lined pool anything below 7.0 can start to do damage to it. Water is easier on your swimmers' eyes, too, in the mid sevens.

From what little I know, your description of the process is accurate, as is you thought to make your final raise with aeration.

Hope you didn't pay too much for the pH Plus! product. I see Washing Soda (same thing) for about $1/lb.

[PoolJunkie]

I was following the instructions on the Pool Solutions website which suggests holding the pH low until the Alk has corrected. Those instructions say no lower than 6.6, or the bottom of the scale for the kit being used. The bottom two tiers on my kit are 6.8 and 7.2, so I have been keeping the color right between those two, probably close to 7.0. I am only doing that for this process and will let it come back up to 7.5 when the Alk is corrected. My goal is Alk 110, pH 7.5.

[PoolJunkie]

So i have gotten my total alk back to 120 ppm using dry acid. I have found that aerating the pool will get the pH back to 7.2, but not much higher than that. I bought some 20 mule team Borax to raise the pH back to 7.5 and if I understand this correctly, this should not affect the TA?

[Watermom]

Correct. The effect of Borax on TA is minimal.