I'm a Little Confused ...

About 6 years ago I stumbled onto this website and learned a lot of good info. Unfortunately for me I haven't been able to access here for a while but have since bought a hot tub.

Here's the confusion: here we adjust the PH first (I least from what I remember) and for hot tubs they have you adjust the alkalinity first. When I use baking soda in my pool the PH doesn't go up as much as it does in the tub. In the pool I need to use borax to get the PH up but in the tub I get to 7.6 easily.

All logic (for me) says that I am using proportionate amounts of baking soda to achieve an alk reading of say 100. Where we use pounds in a pool I use ounces in a tub.

My questions - Why the difference in technique in balancing water between the different industries and why does it seem that baking soda is more "efficient" in a smaller volume.

Thanks!

Vinny

You didn't specify the construction material of the pool and spa but let us assume you are talking about a plaster pool and an acrylic spa. With plaster you will aready have a buffer system going from the dissolving plaster and the acid used during startup and curing. With an acrylic spa it is all dependant on your fill water. As far as the amounts needed a given amount of sodium bicabonate will add a given amount of alkalinity to a given volume of water whether it is a pool, spa, or your bathtub! Unless the pH is WAY out of whack it is better to adjust the alkalinity first which will make it easier to maintain a given pH. I might be new at owning a pool but I have owned hot tubs and spas for many years. The biggest difference is in the amount of water so you have MUCH less room for error if you add too much.
A difference of as little as a teaspoon can be the difference of a properly balanced spa and one that is out of whack! Also the high water temperature and constant airation can also have a big negative impact on your alkalinity while possibly causing a rise in pH with such a small volume of water. In short, the larger the volume of water, the more forgiving it is.

My pool is an AG, so it has a vinyl liner.

I've been using Ben's method now for 5 years in my pool and was surprised when my PH was adjusted so easily by the baking soda in my tub.

I do realize that the volume of water makes a big difference.

Before I had my pool/spa combo built I had a stand alone hot tub for many years using bromine. The biggest problem I had was that the constant airation would tend to cause a pH rise while lowering the alkalinity. What worked for me (after MUCH trial and error) was to adjust the alkalinity first and then lower the pH to the upper end of acceptable (I shot for about 7.6) After reading the FAQ on how to lower total alkalinity here on the forum (before the GREAT CRASH of 2006!) I realized that I was probably doing the right thing. Once again, with the small water volume in a spa it becomes crucial to know the exact amout of water as posible because your dosing might be in teaspoons insead of ounces!

Actually, I have the best water for my tub with PH 6.8 and ALk really low. Using baking soda I get the PH to come in at 7.6 and my alk to about 130 - 140. I usually get my PH in line and don't worry about the alk.

My PH and alk don't drop for weeks and when PH hits the 7.2 mark, I adjust again and the cycle starts again. My pool Alk stays pretty constant and I use borax to raise PH.