ALK vs P

[skylark350]

I may be doing something wrong but...

I find when I adjust the ALK  (tap water is 30) and then have to lower PH (tap water is 7.8-7.9) but when I lower the PH to Alk also comes down.

I seem to be adding chems with one fighting against the other!

Any advice would be appreciated.

Thanks

[Vinny]

My advice would be to adjust PH to 7.4 - 7.6 and see how it stays. Usually low alk will make the PH "bounce around".  Since your water is naturally high with low alk maybe it would stay pretty consistent. Test the water on an every day or every 2 day basis until you get a feel for how the water is behaving.

If you use dichlor, it has a PH of 6.8 to 7.0, MPS has a PH of 4 or so; I don't know bromine's PH. If you use products that are closer to PH neutral (7.0) then the less your water will sway.

I usually don't worry about alk but for me it rises as I raise PH.

I hope this helps!

[tony]

My TA generally stays in the 80 range which is low normal.  You are correct to raise TA first and then pH.  The good thing about Alk Up or Spa UP (baking soda) is the pH is around 8.5 I think, so it will only rise that far.  Then you can adjust your pH down.  Be patient and take small steps.

A very wise man on Doc's board (Ken Lewis) said just a short time ago....Think of TA as the truck and pH as the trailer.

[Vinny]

I have a few questions regarding this alk and PH adjusment since I don't have this problem ... Since you're adjusting the alk first and the PH with baking soda will settle at 8.4 or 8.5, at what ALK point does the PH start coming down?

It seems to me that whenever I put too much baking soda that I don't get my PH to come down until the ALk starts to get around 80.

If the water's natural state is high PH (8.0) with low ALk, wouldn't the water try to stay at it's natural state without adding anything and try to get back to it's natural state (water with high PH tries to get back to high and water with low PH tries to get back to low) when chems are added.

Just asking since I don't deal with this problem at all.

[anne]

This is interesting: from a USGS water quality monitoring website.

Alkalinity is a measure of the buffering capacity of water, or the capacity of bases to neutralize acids. Measuring alkalinity is important in determining a stream's ability to neutralize acidic pollution from rainfall or wastewater. Alkalinity does not refer to pH, but instead refers to the ability of water to resist change in pH. The presence of buffering materials help neutralize acids as they are added to the water. These buffering materials are primarily the bases bicarbonate (HCO3-), and carbonate (CO32-), and occasionally hydroxide (OH-), borates, silicates, phosphates, ammonium, sulfides, and organic ligands.

Waters with low alkalinity are very susceptible to changes in pH. Waters with high alkalinity are able to resist major shifts in pH. As increasing amounts of acid are added to a water body, the pH of the water decreases, and the buffering capacity of the water is consumed. If natural buffering materials are present, pH will drop slowly to around 6; then a rapid pH drop occurs as the bicarbonate buffering capacity (CO32- and HCO3-) is used up. At pH 5.5, only very weak buffering ability remains, and the pH drops further with additional acid. A solution having a pH below 4.5 contains no alkalinity, because there are no CO32- or HCO3- ions left.

Alkalinity not only helps regulate the pH of a water body, but also the metal content. Bicarbonate and carbonate ions in water can remove toxic metals (such as lead, arsenic, and cadmium) by precipitating the metals out of solution.

[Vinny]

Thanks anne!

I'd be interested to see how much swing a low alk, proper ph untreated (for PH and alk) tub has. skylark350's PH is almost in range for PH and I wonder if it would drop significantly with use or would it drop somewhat and then baking soda can be used to raise the PH and alk will follow.

Unfortunately, I do need to use baking soda to raise PH. The PH out of my tap is around 6.8. My PH is pretty much rock steady with my routine and when it gets to about 7.0 to 7.2,  I add a little more baking soda to raise the PH.