Water Balance Question

[ddb]

I have been having problems getting Total Alk and PH in synch for the last several water changes so I wanted to see if anyone had any ideas of why this might be happening.  For the first couple of years with the spa (2006 HS Vanguard) I didn’t have these problems.

My water is Lake Michigan water, out of the tap I measure TA of 70 and PH of 7.6-7.7.  I have been using Nature’s Way Alkalinity UP (Sodium Hydrogen Carbonate) and Nature’s Way PH Down (Sodium Bisulfate?).  When I add enough Alk UP to get it into the 110-120 range or so (initially after fill), the PH moves up to 8 and beyond and it’s difficult to get it adjusted down to where it should be.  I’ve had best results just adjusting the pH alone and can get it to 7.2-7.4 easily and it stays there for 2.5 months pretty consistently, with minimal maintenance.  Is there something I am doing wrong or missing, or is adjusting PH alone acceptable?

Thanks for any thoughts.

Doug

[chem geek]

Doug,

A higher TA will result in a faster rate of pH rise, depending on the source of sanitizer you are using (some are more acidic than others).  So you generally want to adjust the TA to the level where the pH is stable.  If that's at a lower TA, as in your case, then so be it.  It's perfectly fine to have the lower TA.

If one needs to get the TA very low, say to 50 ppm, for pH stability because they are using hypochlorite sources of chlorine (bleach, chlorinating liquid, lithium hypochlorite, Cal-Hypo) then one can additionally use 50 ppm Borates for pH buffering (say, from ProTeam Gentle Spa, for example).

Total Alkalinity (TA) is not only a pH buffer, but a SOURCE of rising pH itself due to carbon dioxide outgassing which is faster with at higher TA, lower pH and with more aeration.  It's counter-intuitive, but it's a chemical fact.

Richard

[ddb]

Thanks Richard.  So I will go the route of bringing down the TA and Ph at the same time.  I appreciate your help.

[Vinny]

You don't really need to bring down your PH as it comes out of the tap. Your PH is at the top of the range and that's not a bad thing. Balanced water has a range not an absolute number. If you're using Dichlor or MPS they tend to bring down the PH naturally.

I use only baking soda to raise both PH and alkalinity when my PH falls too low. I've been told by Richard that my PH rises due to the outgassing as he mentioned here. Can't say he's 100% correct (although I do assume that he is!  ) but it works for me and my PH remains pretty stable for a few weeks.

Also remember that water, any water, can change over time depending on Mother Nature or water treatment. Things in your water may be different today than they were just a few weeks ago.