Understanding Chemicals !

[robquick]

Hi,

I'm getting a little confused with the process of reducing TA. On this site it talks about reducing PH with 'acid' to 7.0ppm and then aerating to increase PH.

What exactly is 'acid' ?

I use Sodium Carbonate and Sodium Bisulphate to increase/decrease PH. Do these two chemicals have any significant impact on TA or is 'acid' a completely different chemical ?

Can I buy 'acid' in the UK ?

Thanks.

[chem geek]

Sodium bisulphate is acid, sometimes known as dry acid, so that is what you would use to lower the pH. There are other acids that can be used such as Muriatic Acid, but that's strong stuff (especially the vapors from full-strength 31.45%; half-strength 15-16% doesn't fume as much) so not normally used for spas though it is commonly used for pools.

Sodium carbonate increases TA a lot as well as pH because technically it's the same as a combination of a base (sodium hydroxide) that raises (mostly) the pH combined with baking soda (sodium bicarbonate) that raises the TA. As an alternative, you can use Borax (if you can find it) to raise the pH with only half the amount of rise in TA.

[robquick]

Thanks, really helpful explanation.

Looking through the cupboard I've also a tub of PH increaser which contains Soda ash. How does this fit into the equation ?

[chem geek]

If it's nearly pure Soda Ash, then that is sodium carbonate and raises both pH and TA. You can usually buy some of the common pool/spa chemicals at the grocery store.

Baking Soda (NOT baking powder) -- this is sodium bicarbonate and the same as Alkalinity Up

Soda Ash aka Washing Soda -- this is sodium carbonate and the same as most pH Up products

Dowflake or Peladow -- this is calcium chloride and the same as Calcium Hardness Increaser products

20 Mule Team Borax -- this raises the pH with about half the rise in TA

Muriatic Acid - this is usually full-strength 31.45% Hydrochloric Acid though may be half-strength 15-16% Hydrochloric Acid; it lowers pH

There are also synonyms for pool/spa store products that you have to get there or from some big box stores.

Dry Acid -- this is sodium bisulfate and the same as pH Down

You can get some chemicals from websites selling chemicals for making soap or at other chemical websites.

Boric Acid -- this can be used to add 50 ppm Borates; sometimes found in ant/roach killer products

Caustic Soda aka Lye - this is sodium hydroxide and can be used to raise the pH with half the rise in TA (Borax is easier to handle and store)

[robquick]

Just a thought but the 'AKA' for chemicals that you've listed above is really helpful for people like myself that are new to hot tubs. Is there any chance a comprehensive list could be put together and added as a 'sticky' ?

I appreciate I'm volunteering someone else to do the work but it would be really helpful !

[robquick]

ChemGeek,

I have a few questions I would appreciate your help with.

Is TA 'up' always the same chemical ?

Am I right in assuming that TA increaser has little impact on PH ?

When using the Dichlor/Bleach method the recommended TA is 50ppm, I know it's safe to have the TA at this level however, what's the theory behind it as all Spa manufactures recommend safe levels being 100-120ppm ? Apologies, I have asked the question before but I can't remember the answer !

Thanks.

[chem geek]

Alkalinity or TA Up is always baking soda as far as I know. pH Up is sometimes soda ash / washing soda / sodium carbonate but sometimes baking soda / sodium bicarbonate is sold as pH Up, especially for spas. Baking soda will raise much more if the pH starts out low. Otherwise you are right that it doesn't raise the pH that much if it's already closer to 8 while pH Up if sodium carbonate will raise the pH regardless of its starting point (well, until it gets closer to a pH above 13!).

Spa manufacturers do not recommend bleach; they usually recommend Dichlor. Since Dichlor is net acidic, it needs a higher TA to have carbon dioxide outgassing (which raises the pH) to balance that out so that you get a roughly stable pH with a slowly decreasing TA for which baking soda can be added. Also, not everyone understands that TA is a SOURCE of rising pH. Many people just think of it as a pH buffer and forget that the water is over-carbonated. Because we recommend a lower TA with the Dichlor-then-bleach method, we also recommend using 50 ppm Borates for additional pH buffering but without the side effect of carbon dioxide outgassing that causes the pH to rise.