muratic acid suspension

[carlos31]

I tried asking this same question in another thread but I think it probably belongs here. Only a chemical guru probably has a shot at this one.

I will be doing an acid start-up on a plaster pool and adding 1 gallon of acid per 2500 gallons of pool water. United Chemical says brushing the pool once a day is sufficient to maintain the acid in suspension. The plaster company thinks the main pump should be running (or sump pumps) to not only mix the acid into the water but also to prevent the acid from coming out of suspension and collecting in the deepest part of the pool.

It just kills me when experts have such varying opinions. :?

Who is right?

 

[chem geek]

I am totally confused by this "suspension". Though it is absolutely true that Muriatic Acid is denser than water and will settle to the bottom if you don't mix it, once mixed with water it stays mixed. When mixed with water it is not in "suspension", but is more like dissolving salt in the water -- it stays mixed as ions in the water. "Suspension" is usually applied to items that don't mix or dissolve into each other, like oil and water, that when mixed will tend to separate. Emulsifiers and other chemicals help such items stay mixed together longer, but they eventually separate.

Muritatic Acid itself is NOT pure hydrochloric acid but is a mix with water with only 31.45% being hydrochloric acid. It does not settle or fall out of suspension because it never was in suspension.

[EDIT] See posts below and ignore my advice about running the pump. Do not run the pump, but do brush to mix the acid with the water. [END-EDIT]
So running the pump while adding the acid and even lightly brushing the side and bottom where you add it to ensure thorough mixing makes sense. Once it's mixed in the water, then this is out of my league since I don't know what is best for plaster curing -- good circulation or still water -- since other physical factors come into play and I'm just into chemistry. :-D

Richard

 

[mas985]

Generally in acid starts you don't want to run the equipment since the PH and alk is so low. The point of an acid start is to make the water very corrosive so with the addition of a lot of acid, Alk gets close to 0 and PH is very low (<<6 ?). Because the acid is dissolving the plaster dust, PH and alk should climb fairly rapidly but I would not start the equipment until they are in accepted ranges.

 

[Denali]

Equipment off and brush. MA doesn't fall out of suspension. Once mixed with the water it lowers pH. If it were somehow in suspension you would never be able to turn off your pool equipment.

I would follow United's instructions. This procedure has been around for a long time.

 

[carlos31]

I appreciate the advice. The plaster company doesn't perform start-ups. My guess is that they have been called back to damaged plaster where the acid was added but not properly mixed. Since they don't monitor the process they probably assume the acid comes out of suspension unless constantly circulated, which seemed reasonable to me until I was educated. Thanks!

Unfortunately, I can't buy United Chemicals products since they only sell via SCP or SPP and I can't get a business account with them. This leads me to three additional chemical questions.

1. I will need to purchase a sequestrant/chelating agent. I assume one that favors calcium. Can anyone recommend a brand available at pool stores?

2. Instead of phUp, I can use borax, baking soda or soda ash. Does one make more sense than the others?

3. How long should the plaster cure before adjusting borates to 50 ppm? I will be neutralizing alot of acid anyway - can I just go ahead and take the pool to 50ppm borates by using borax to neutralize?

thanks.

 

[JasonLion]

1) Jack's Magic The Blue Stuff is a wonderful sequestrant that is ideal with fresh plaster. There are many other choices, that is just my personal favorite.

2) Soda ash and PH Up are the same thing. Borax is just as good for raising PH. Baking soda is not a good choice, as it will increase the TA way too much.

3) It is best to wait a month after plastering before raising the borate level. You can use borax to control PH right away, but in the normal course of events you won't use nearly enough to get to 50 ppm of borates.

 

[carlos31]

thanks,

plaster day is Saturday, any opinions on how long the sequestrant should be in the water before adding the acid? I haven't bought it yet, so I don't know if the label instructions will be helpful.

also, the pool store tested my fill water

ph 7.4
TA 285
CH 201

no wonder my water is hard!

 

[carlos31]

I used Jack's Magic Blue at the label rate and added the acid the next day. My PH is below 7 and TA is 160. I am going to increase my acid level from 1 per 2500 gallons to 1 per 2000 gallons. The dust still seems strong and I believe the TA should be much closer to zero during an acid start.

I am already sick of brushing the pool.

 

[carlos31]

I neutralized the acid and I am working on the water balance for which I will start a new thread. I guess the acid start was useful but it wasn't a cure all for plaster dust. There is still plenty of it in the pool. The 4x160 and the Quad DE 100 will need to get the rest of it.

Did I mention we are sick of brushing the pool?

 

[JasonLion]

Good to hear that everything is moving along for you.

There is almost always some plaster dust. You should see how much there would have been if you hadn't added any acid.

 

[carlos31]

Lats night I purchased a small triangular vacuum head made for vinyl pools. It has the same brushes that are found on a regular pool brush. The 4x160 is running on preset 4. I hooked it to a skimmer port, shut down the main drain and one skimmer, then swept the entire pool with this head (about 10 inches wide). It took 2.5 hours to cover the entire pool but it sucked up nearly all the remaining standing dust in the pool. I will be cleaning and recharging the Quad DE100 shortly.

still brushing...