Raising pH with sodium hydroxide

[skinpath]

Every once in a while I need to raise the pool's pH a little, but quickly. Aeration takes a long time and with the size of my pool it doesn't really work well. So I use Borax, which works pretty well, but is cumbersome.

Would there be a problem with using a sodium hydroxide solution, instead of Borax, to raise the pH? I figure I could dissolve solid sodium hydroxide and make a stock bottle of concentrated solution and use it the same way I use muriatic acid to lower the pH if it gets too high.

Thoughts?

 

[JamesW]

Dissolving sodium hydroxide is highly exothermic. So, the solution will get quite hot when the sodium hydroxide is added.

Sodium hydroxide is quite hazardous and should only be handled by someone who knows how to do it safely.

It will raise the pH quite a bit with minimal TA rise.

In general, I would advise people to avoid dealing with it in favor of something safer.

If your pH is going too low, you can raise the TA and the pH will not drop.

 

[ajw22]

What type of situation causes you to need to quickly raise the pH a little?

 

[borjis]

It actually seems much more complicated not to mention hazardous, than just dosing some Borax.

 

[duraleigh]

Skinpath,

Something else is going on here. There is no "cumbersome" to using borax. Your idea is much more complex and unnecessary. What's up?

 

[skinpath]

I'm finding that my pH tends to trend downward in general. I know it's generally supposed to trend upward, but it doesn't. The first couple of years it occasionally trended upward, but this year it pretty consistently trends slowly downward. It may be because we don't use the pool as much as before, so it doesn't get as much aeration. The liner was also changed this past year, although I wouldn't expect that to have much of an effect on pH. I use liquid chlorine only. I've been thinking about what might be causing the slow drop in pH, but haven't been able to come up with anything. Maybe its the pool's way of telling me to use it more often .

Anyway, because of the slow downward trend in pH, i'm often finding myself in situations where the pH is getting down to 7.2 and I want it around 7.5-7.6. That takes most of a box of borax and, because it's a solid, I feel like I kind of have to sprinkle it around the edges of the pool or dissolve it in warm water and then pour it in front of a return. Also, if I keep a box of borax for too long, it tends to clump up, which makes it harder to distribute or dissolve. It's not a major problem, but TFP has made every other aspect of maintaining the pool so easy that adding solid borax seems a pain by comparison . I've tried putting a sprinkler-type attachment on one of the pool returns to make bubbles and help aerate the pool, but it doesn't really help much and, of course, it only works while the pump is running.

When I did have to LOWER the pH in the past, I used concentrated muriatic acid, which required relatively small amounts which I could pour in front of the return and quickly disperse in the pool. Plus, every so often the wind would blow just right and I'd get a whiff of the acid, which would bring up fond memories of chemistry lab (don't judge). That's what made me think of the sodium hydroxide solution. Doesn't sound like a very popular idea, though...

BTW, my current TA is 130 (pH is ~7.6), so I don't think a low TA is causing my problems.

 

[JamesW]

It doesn't make sense for your pH to drop with a TA of 130 and only liquid chlorine being added.

For the pH or TA to drop, you would have to add something acidic like trichlor or muriatic acid. Or, you would have to be replacing water lost to a leak with low TA and pH water.

Does the TA tend to drop as well as the pH?

Do you use trichlor or acid?

A pool cover can reduce or eliminate pH rise by preventing carbon dioxide from outgassing, but it won't cause the pH to drop.

In any case, if the pH is constantly going too low, a higher TA will prevent it from happening.

 

[cfherrman]

Use the ta+pH up chemical we use (baking soda? Or is soda ash?) To raise your pH and see if it will find a setting point. You should play with pool math a both to make sure extra points of ta won't mess your csi up, you can balence your csi with ch and salt if need be.

Also double check your pH test ing methods just to make sure no testing error

 

[Donldson]

I agree with James above, at 130 TA water should only be suffering from pH drop if an acid is being added. Even pools that use trichlor tablets (with a pH of 3) and a TA of 130 rarely deal with the pH dropping.

As far as dealing with it though, soda ash is the best option if a significant pH increase is required. It is not only a more potent of a base than borax but also raises the TA so if there is a source of acid being added that cannot be controlled (acid rain, acid fill water, etc) the increased TA will help buffer this. Ideal TA range is kind of a misnomer, what is ideal is the TA that keeps your pool water most stable. It varies from pool to pool.

EDIT: Just wanted to add that soda ash is sodium carbonate/washing soda. It is likely right beside the borax in the laundry aisle. Same thing as the more expensive pH+ products you find in the pool aisle.

 

[duraleigh]

Sodium hydroxide aside, I would like to learn how OP has a pool with a tendency for pH to lower.

Skinpath, what is your source water pH? How do you chlorinate?

 

[skinpath]

Thank you everyone for your input - this is one of the reasons I love TFP.

I use tap water to fill (I checked and it's pH 7.5), although I’ve barely had to add any because of the relatively wet summer. Could it be due to acidity of the rain water?

I chlorinate with liquid chlorine only (pool essentials chlorinating liquid from the local Walmart - it’s 10%). I only use chlorine tabs on the rare occasion (only once this summer) when everyone is away for more than a few days - but this slow fall in pH happens even when I'm not using the chlorine tabs.

I do use a solar cover and it’s almost always on the pool when the pool isn’t being used.

Possibly related - I’ve noticed that the pH of the pool is typically low when I open in the spring. It’s always 6.8 or less and based on how much borax I have to add when I open, I would estimate it’s about 6.5. I have a mesh safety cover and I open early (this year I opened in mid April).

 

[duraleigh]

When I did have to LOWER the pH in the past, I used concentrated muriatic acid,

How long ago was that? What has changed since then? Did you report your TA anywhere above?......I didn't see it.

 

[JamesW]

The basic fact is that the pH won't just drift down on its own. Something acidic has to be added.

Does the TA also drift down?

If the pH and TA are drifting down, you're missing something that's going on.

 

[skinpath]

How long ago was that? What has changed since then? Did you report your TA anywhere above?......I didn't see it.

I used muriatic acid in previous seasons, not this year. The only thing that I'm aware of that changed since previous seasons is the new liner.

My TA is 130 and doesn't change noticeably. But I'm also adding Borax every once in a while, which would tend to increase TA a little.

The basic fact is that the pH won't just drift down on its own. Something acidic has to be added.

Does the TA also drift down?

If the pH and TA are drifting down, you're missing something that's going on.

I agree, just not sure what it is...Would low pH rain be enough to do it? Could my liquid chlorine be acidic? Maybe my testing isn't accurate enough (we are talking about a pretty narrow range of pH) - I use the standard OTO kit for pH, but maybe I should try new reagents and / or an electronic pH meter. How well do those electronic pH meters work?