What's up with muriatic acid?

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draythomp

draythomp

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Jan 26, 2011
40
I've had my pool for 5 years with it's SWG. At first, I would water down my acid to clean the generator and it worked just fine, and now it isn't. A little background, I'm in the desert and the calcium content is very high so the generator needs to be cleaned often. Sometimes as much as once a week. After a few acid cleanings I decided that much exposure to acid had to bad for it so I went to washing it out with a 1600 pound pressure washer. This worked well by just blowing the white stuff out of the generator. I did have to occasionally (6-8 months) acid wash it to get it back into shape though.

Then, one time when I dunked it into the acid I noticed it didn't bubble. There was white stuff in there, but no bubbles from the acid. The big stores here carry muriatic acid that is rated at around 15% so I started going to Leslie's for their 29% stuff early on. But now they are selling "White Muriatic Acid" This stuff is clear (no yellow) and doesn't fume very much when opened. And even a concentrated solution of this stuff won't bubble in a generator that has a lot of buildup. When I dump the residue on the alkaline ground here it bubbles a lot.

Have the physical laws changed recently and I missed the memo? What is White Muriatic acid? I know that the stuff used in special applications can be clear (no yellow), but the acid used in industry is normally a nasty yellow that fumes and causes your nose and eyes to burn. I hate to go to the stuff from Home Depot because I pay for half concentration at a tiny amount less money. Note though that I haven't tried the Home Depot stuff for cleaning in a couple of years; it may work.
 
It sounds like you are describing that "fume free" stuff that is out there for people who don't like messing with the strong 31% stuff. Without knowing the strength and the full composition of it, I wouldn't use it for pool purposes.
 
I'm also in the desert, Tucson to be exact. That "white MA" at the pool store I think is 30%. I've been buying MY 31% MA at Ace Hardware for only a bit more than the 15% at Lowe's or HD.

I also had to clean my SWG often. But once I got my water in balance, added borates and made very sure to keep my pH from getting to high, I haven't had to clean it at all. When the inspect light goes on I pull the cell and check it, but it's always clean.
 
It could be the same as the fume free your talking about, I haven't seen that yet (thank goodness). But the contents list is only muriatic acid and "inert ingredients". The concentration claims to be 29%, but if it won't boil the stuff out of my chlorine generator, it couldn't possibly be that high, unless one of the inert ingredients is NaOH. I've just recently (this year) learned about the importance of keeping the ph down. I even went so far as to build an acid injector that pumps it in for a few minutes from time to time. However, if it isn't acid..... I checked the Leslie's site and they don't even show the stuff my local store sells. They do mention that the HCl in the Southwest is different from the rest of the country, but don't say how.

I do not have borates in the pool, and that actually sounds like what I should do. It's gonna be tough getting enough borax though, the stores only have 4-5 boxes of 20 mule team on the shelf, I'll start stockpiling it over time.

And, thanks for the lead on the acid at ACE hardware. I haven't checked there. I go there for plumbing parts from time to time so it wouldn't even be inconvenient to look into it.

Fume free HCl??? There just something terribly wrong about that. And, why do they sell the 14% stuff at the big outlets? Is there some new law that only applies to them?
 
You might try the paint department at the big box stores for the acid. At my lowes they have a bunch of acid in the pool section but it is only half strength. In the paint section they usually have a few bottles on the ground of the full strength acid. They will also have the half strength acid mixed in there so I make sure I read the labels to get what I need.
 
draythomp said:
I do not have borates in the pool, and that actually sounds like what I should do. It's gonna be tough getting enough borax though, the stores only have 4-5 boxes of 20 mule team on the shelf, I'll start stockpiling it over time.
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As noted in Recommended Pool Chemicals, you can get boric acid online. Though more expensive than 20 Mule Team Borax plus acid, it won't require any addition of acid.

The borates help to prevent scaling not only by slowing down the rate of pH rise, but by lessening the amount the pH rises in the salt cell itself.
 
Melt in the Sun, just for an example, I took the generator off, wrapped one end in plastic and wrapped an elastic band around the plastic to hold it on and poured straight 29% Leslie's White Muriatic Acid in the cell about a third of the way up. No bubbles, so I went half way, no bubbles. Filled the darn thing up and still no bubbles. This is right out of the bottle, no dilution at all and no bubbles. The cell was loaded with white encrustation and the stuff just sat there doing nothing. Oh, there was the occasional bubble or two that worked its way to the top, but not the raging foam that would bubble out the top like the old days.

So, either the acid is strange or the material has changed into something else that doesn't react. I haven't seen any chemistry discussions on what besides the usual calcium stuff that could be adhering to the plates, so I'm blaming the acid. Although, when I pour the acid on the ground, the caliche impregnated soil I have will bubble and turn green.

Could it be that there is something else collecting on the plates?

The problem I have with ordering the borates is that the quantity I need always seems to cost a bunch in shipping. I'll take another look for a supplier, but Phoenix doesn't seem to have an abundance of chemical supply houses since there's not a lot of industry here.

I'm not one of those folks that whines and complains, finding excuses for not doing something; I don't mind accumulating the borax a corner of the garage until I have enough to do this. It just takes more time that way, but the pool isn't going anywhere and I assume it will still be in the yard a couple of months from now. :p

I think I'll go to Ace today and get a box of their acid. Then I can experiment with the cell and see if the different acid behaves differently. If it doesn't bubble in the cell, then the white material on the plates is different and might need a different cleaning technique. Although, I just cleaned the cell and there may not be enough build up to do this until next week or the week after.

Anyone heard of a different white deposit on the salt generator plates? I always assumed this was calcium carbonate, and never thought about some non calcium deposit.
 
draythomp said:
Could it be that there is something else collecting on the plates?
Click to expand...
I think that's the only explanation for what you're describing. The fact that it bubbles on your caliche proves that the acid is fine. As for what could be in the cell, I don't know...perhaps a picture of it could help?
 
I absolutely would take a picture if hadn't cleaned the cell recently, but it's just a white build up like that looks exactly like the stuff you see in all the pictures of dirty generator cells all over the web. Sort of like the build up on the walls of a pool that we deal with over time except between plates of the generator instead of on the wall of the pool. Back in the good old days when it would bubble, it looked exactly the same as now.

That doesn't mean anything though, there's lots of different kinds of white stuff. I'd post my water balance numbers, but I don't have the kit yet. I suckered into believing the pool salesman's spiel about test strips being the best way to go and have been using them. After prowling this board looking for leads on this problem, I realized I needed to get a real test kit and am waiting patiently for payday to order the darn thing (pricey little item).

Pool's are expensive. And I refuse to hire one of those companies to do it for me until I can't do it myself anymore.
 

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Just to annoy y'all, I went to ACE hardware today and checked out their muriatic acid. It was exactly the same as the stuff at Leslie's. White Muriatic Acid 29%. So, my problem must be that what is collecting on the plates of my salt generator cell is not calcium carbonate any more. There are other forms of scaling, but I haven't found out what they are. It must be silicon based because it just laughs at 29% HCl, and since I don't have a GC-MS in my garage, this may be hard to figure out. :?

I also stopped by Leslie's and had them test my water. Seems I ran the pool out of CYA, its level was zero, but nothing other than phosphates was strange. CYA is dissolving in the pool as we speak, but I'm not any closer to an answer about the white stuff collecting on the plates. Going to Wally World tomorrow, I have a couple of them in driving distance to pick up some 20 Mule Team; who knows, I may luck out and get enough. Need the test strips though, gotta remember that.

Oh, while I was there they told me that my salt level was 2900. I told them I just tested it a few days ago with the reagent test and it was 4000. They said I must have a leak that was dropping my salt level. So, when I got home I rushed out and checked the salt level again. Yep, 20 drops times 200 a drop; exactly the same as my test last week. Stupid electronic meters at pool supply places. Never trust those things.

So, who's the expert on white powdery stuff that resists HCl in high doses?
 
I used 14 boxes of 20 Mule Team Borax to borate my pool. The local Walmart only had 10 on the shelf but I just stopped at a supermarket on my way home and bought 4 more.
 
Best indication is that the white crust I've been fighting is calcium sulfate and not calcium carbonate. They're both common and especially in my soil. When I got a hint at what it might be, I evaporated some water out of a glass which took about a minute here in the sun at 109 F and then rinsed the glass with some of the HCl and dumped it out. After letting the glass dry again (another minute) there was a scale in the glass. Ok, so that should be reproducible somewhere else so I got the outside dog bowl and tried to dissolve the scale off of it. Some went away, some didn't. This also explains how difficult it is to clean the scale off the toilets in the house (gross, I know, but true).

So, for folks out here in the desert with alkaline soil, watch out. The various cleaning instructions may not work for you. The scale you see in your chlorine generator may be more resistant than you suspect. Makes me wonder if I should start researching a method of cleaning these things that is more mechanical. Maybe a small bottle brush or an orange wood stick to actually scrape some of the stuff off. Aqua Regia? maybe (kidding). Actually, dishwasher detergent or one of those water spot removers might do the job.

But, at least the mystery is solved.
 
If you ever used dry acid or non-chlorine shock, then these add sulfates to the water in addition to whatever you started with in the fill water. The solubility of calcium sulfate is such that you'd have to have rather high sulfate levels to get scale. With a CH of 300 ppm, the sulfate level would have to be 3500 ppm to get scale (at 600 ppm CH, then 1600 ppm sulfate can produce scale). So it's good to know that calcium sulfate scale is so difficult to remove. Thanks for letting us know.
 
Thank you very much.

I'm working from memory here, so I may mess this up. The water here has a very high CH, around 1000 or so (well water). So, just starting out we're way above recommendations and changing the water doesn't change anything. So, your notes on solubility make perfect sense. My suspicion is that I've been removing the calcium carbonate by cleaning it out in the filter as the chlorine generator precipitated it on the plates and spit it out into the pool where the filter eventually got it. Now that a lot of the 'easy' stuff has been collected, I'm into the sulfate and starting to have trouble getting rid of it.

That's ok though, as long as it has an explanation (I hate not knowing). It only takes me thirty minutes or so with the power washer and maybe some mechanical aid in the future to get the stuff out so I can live with it.

One question for folks in general though. The SWG is perfect for crystalizing this stuff; the hot, caustic environment in there causes the material to drop out of solution and be thrown into the pool (at least what doesn't stick to the plates). It would be so cool if there was a filter that we could use to catch this stuff and clean reasonably often. That way we could remove it from the water and get the CH levels down over time. So a smaller, cartridge filter that won't restrict the flow and is easy to open and clean would be really cool. I have a big 4 element cartridge filter and it's a pain to clean, and the stuff drops into the pool and sets there on the bottom waiting for me and a vacuum to come along.

suggestions??
 
Unlike calcium carbonate, calcium sulfate solubility is independent of pH. So I'm not sure why it seems to scale in the salt cell, but would also explain why acid doesn't have very much effect at removing (dissolving) it. This BioGuard link (which should be taken with a grain of salt, pun intended), notes that calcium carbonate scale is the most dominant, followed by calcium phosphate and then calcium sulfate. This link refers to the salt cell blades getting hot which would explain how calcium sulfate scale might form since it is less soluble at higher temperatures (scaling in a heat exchanger would also be a problem), though actual charts would indicate that this is primarily seen above 40ºC (104ºF). So it's more likely that calcium carbonate scale initially forms and causes the blade temps to get even hotter and then calcium sulfate forms and is hardest to remove.

You noted that the CH level is 1000 ppm so a sulfate level of around 900 ppm or more could produce scale at normal pool temps.

Probably the easiest thing to do is to find a way to reduce the CH level. I don't think it is easy to lower the sulfate level. Options include using a metal sequestrant optimized for lower CH and preventing scale, precipitating/filtering calcium out (more on this later), reverse osmosis, dilution with water lower in CH. As for precipitating/filtering out CH, that is tricky. If you were to add a base to the skimmer, or even washing soda (pH Up; sodium carbonate), then calcium carbonate would likely form a cloud of precipitate that would get caught in the filter. The problem is trying to make sure that this calcium carbonate primarily collects in the filter and doesn't form scale elsewhere in the system including piping and pool surfaces (for what doesn't get caught in the filter). The good news, is that lowering the pH can reduce fresh scale that has formed and you can use acid and aeration to lower the TA back down (if you used washing soda). This is not something that has been done as a procedure on this forum so is risky.

As for your idea of having a small filter downstream from the SWG to capture the flakes of calcium carbonate, that's not a bad idea. Probably the main reason that isn't done is that the filter would have to stand up to the stronger chemistry coming out of the SWG -- the same reason the SWG is put after any heater. The chlorine level is higher, but more importantly, there is strongly acidic and strongly basic water that isn't yet thoroughly mixed. Of course, one could put some sort of efficient mixer after the SWG, but that's generally not the approach taken.

Another possible calcium reduction technique that's been talked about is to use sodium oxalate since that forms a calcium oxalate precipitate and excess oxalate can be removed by chlorine producing carbon dioxide. This has happened unintentionally as described in this thread during a metal stain treatment so is not a honed procedure done on this forum so is risky.
 
I really, really like the idea of sodium oxalate. Yes, it would cloud my pool and make a mess, but that's what filters are for and when it lowered the calcium level through precipitation and filtering, I would be in really good shape. See, my pool started off at 1000, but through evaporation and addition of water over the years here in the desert, it will continue to increase. Changing the water just delays the problems and doesn't really resolve anything. I should be looking for a maintenance solution. Think of all the other desert rats with swimming pools that could benefit from a method that could help with this.

So, here's my plan, I'll look for some sodium oxalate and do a small experiment. I'll just use a few ounces and see what happens. It's just me around here right now so the only people inconvenienced would be me and a couple of dogs. Right this second I can't test for CH, but that can be fixed. And, I'll hold off a bit on adding borates until I can try this out. A little testing could save me a big bill getting a truck out of town to add water that really won't help much.

Assuming this works, there are techniques I can use to make it easier in the future, inject the oxalate in front of the filter (down the skimmer maybe) and let it catch it early, set aside a week in late winter to treat it for this kind of thing, etc. The trick is knowing what to do and what happens when I do it. I found a place here in south Phoenix that will sell me this stuff by the pound and I'll drop down there early next week and pick up some .

Now, I also like the idea of post generator filtering. Sure, the environment will shorten the life of a filter, but If I can find a small filter that won't restrict the flow, that may not matter. Suppose I get a single cartridge filter of some kind and plumb it in. However, if the experiment above works, I don't need it.
 
I haven't actually priced the mobile alternative, but I live a little over 30 miles from there at the end of a mile of dirt road and am on a well. I suspect we're talking several hundred dollars to get this done. It costs me roughly $300 to get the pool filled, so the math kinda sucks. Additionally, once it's done, my summer evaporation rate seems close to an inch a day during the peak. I probably add about a pool full of water back in over a years time and would be back in exactly the same state in short order. The home device is intriguing but the smallest device is over $3000 if I install it myself and it dumps about half the water it processes out a waste tube. I have an RO for drinking water and it's amazing how much water it dumps into the septic tank.

Alternatively, if my experiment works, there will be a documented way to reduce calcium with minor inconvenience and at the owners leisure. It'll also give me a way of maintaining it over time and not have to call somebody out. I realize a lot of you folk that are helping me are in the business, but once when I was looking to get a pump installed, I got several quotes for the work. First the pump price varied by over $500 between dealers and all of them, except one, wanted to charge me to come out and give an estimate for installation. The one guy that didn't charge for the estimate wanted the most for the pump. The average price to come out was around $60. I got the pump for $500 (after the power company rebate) and installed it for about $20 in two inch fittings and glue. Hayward even sent a rep out to take a look at the installation and update the controller software for me. Later, I added an acid injector to keep the ph under control and modified the solar heater to work under the very low pressure of a variable speed pump.

So, it appears the DIY methodology works really well for me. I've probably already saved the $500 expense in power for the new pump and didn't have to listen to a plumber tell me how badly the last installation was done while watching him go to the store twice for fittings he didn't have on his truck.

Please don't misunderstand. My experience is not indicative of the industry in general. There are lots of honest folk out there that do a really good job for a fair price; I just have trouble finding them.
 
Just keep in mind that trying to control where precipitation occurs and trying to do so without causing general scaling damage is tricky. So you are definitely on your own experimenting with this, but be sure to let us know what happens as this is how new techniques are often discovered. I'm hopeful that calcium oxalate is less likely to scale where you don't want it, but we really don't know for sure.
 

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