Adding Muriatic Acid directly to skimmer

[AUSpool]

I added acid to my skimmer once, only once. I noticed a plume of dust comming out of the return jet and thought 'don't do that again'. Before finding TFP I had always done what I thought was best practice and diluted my acid in a plastic watering can and broadcast it around the pool surface with the pump running. I now feel I'm being a little lazy when I slowly pour it in front of a return.

|Edit - I keep thinking about this and wonder which method would ultimately mix the fastest, a full plastic bucket of diluted acid / pool water poured in slowly in front of a return with the pump on, a full plastic bucket of diluted acid / pool water poured in evenly arround the parimeter of the pool with the pump on or a full plastic watering can (same volume) of diluted acid / pool water broadcast over the surface of the pool with the pump on? Return, poured or broadcast? I'm thinking it would probably be in that order, return, followed by poured, and then broadcast. Any thoughts?|

 

[BobDenny2]

Let me explain what you're seeing and why your experiment is wrong.

Muriatic acid, like all strong acids, attacks and removes the passivation layer on metals, that is the metal oxide film. So on your copper pipe, the minute you placed it into muriatic acid, the copper oxide is removed and, at extremely low pH (the pH of 20 Baume MA is -1) pure metal surfaces are stabilized. The metal itself will only very slowly dissolve in pure acid, the rate is typically to low to measure over short time spans. You can see this PDF document on etch rates of various materials and etchant types used in the manufacturing of MEMS devices (MEMS are Micro-Electrical-Mechanical Systems and the air bag accelerometer sensor in your car is an example of a MEMS device). In the acid solution, the metal will not re-oxidize. The process you are performing is called "pickling" in the metal finishing industry and it is used all the time to clean and remove unwanted oxide films and chemical impurities from finished metal surface. Once the surface is exposed to air (or neutral pH water) and new oxide passivation layer will form. If you want to do a real experiment, you would have two containers, one filled with acid and the other filled with water. Then you would cycle them back and forth and you would, after many cycles, see and measure a fair amount of copper loss.

[EDIT] A better experiment (to avoid acid drag-out contamination of your rinse water) would be to use a container of MA and a garden hose. Dip the copper tube into the acid for 1 min and then rinse it completely with the garden hose. Repeat that process. After some time, you will see the surface become roughened and the Cu loss will be more apparent. [END-EDIT]

This is exactly what happens in your pool. You spike your pH with acid, it removes the copper oxide passivation layer, and then as the pH is restored, that layer reforms. This cycle is what destroys the heat exchanger.

If you want to do and experiment, make two beakers - one dilute acid (5:1 with water) and the other one with the same dilution and an small amount of hydrogen peroxide added. Add two identical pieces of Cu tubing. You can witness and record what happens to the copper when an oxidizer is present to reform the passive oxide layer.


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Matt, thank you for providing a really excellent response. Exactly what I was hoping for. It is really great that we have an experienced scientist on this forum

I did perform your proposed experiment. 2 vessels of 1:4 MA to water, with one having some hydrogen peroxide.

I’ve included some time lapse pictures, but I need to add that at 1 hour, 4 hours, and 7 hours I added more MA and HP to the glass on the left. I assumed some of the acid was getting used up

Basic finding is that yes, the glass with MA+HP turned green and showed noticeable pitting in the copper. Neither showed any level of real damage over 8 hours of exposure though.

So I ask the chemists again: what is the real risk of pouring MA into the skimmer? I have been doing this for more than a year, about 15 seconds per week, and NOTHING has failed. Someone mentioned a shaft seal failing? This has not happened to me

I tried to upload pictures but the website says they are too big

 

[pooldv]

Check step 6 of this, Re: How to clean a cartridge filter

And what is your reason for not pouring it in front of a return. I have been adding acid in front of a return for 4 years and haven't damaged anything. :-D

You can upload pics to Photobucket, copy the IMG code to the right of the pic and paste it in your post. That will embed the pic into the thread.

 

[BobDenny2]

Check step 6 of this, Re: How to clean a cartridge filter

And what is your reason for not pouring it in front of a return. I have been adding acid in front of a return for 4 years and haven't damaged anything. :-D

You can upload pics to Photobucket, copy the IMG code to the right of the pic and paste it in your post. That will embed the pic into the thread.

]

You apparently didn't notice the prior posts: I don't have a "normal" sidewall return, but all of mine are bottom of the pool pop-ups

 

[pooldv]

You are correct, I dove into the middle of it. It would still be fine to add acid into the pool with the pump running. The reason for adding it in front of the return is to push it out into the pool and mix it so it doesn't drop the the bottom and sit there. Seems like pop ups on the bottom would do an even better job of that.

Is your location a surprise? Or is that really a city? Why no state listed?

 

[wjr75]

I add chlorine to my skimmer once in a while because of our pool cover but I would never add MA to it. I wouldn't try it but let me know how your experiment goes if you try.

 

[max2k]

I think you're missing couple points- heat exchanger is not the only piece of equipment in the pool and all of that machinery fails on its own. Adding concentrated MA will speed up the process, sometimes drastically. Almost none of the pool equipment is designed to withstand concentrated MA. You took just one element from the system and trying to generalize the case while I wouldn't be much happier if instead of heat exchanger my pump seal would fail. Some of the components will probably survive but I'd expect many would not. It would prove your point about heat exchangers but I'd end up with a problem on my hands anyway. BTW if the heat exchanger develops pinhole leak it wouldn't make me any happier to know that the rest of it is 'fine'. These cavities tend to be eaten through quicker than smooth metal- once started it might develop into the hole much quicker than the rest of the pipe. This will also depend on impurities of the copper used. If it was my pool I'd dilute it but it's your pool- your call.

 

[pooldv]

The forum is slow tonight and this piqued my interest a bit. Here is a pretty good discussion, Adding Acid Via The Skimmer

 

[JoyfulNoise]

The forum is slow tonight and this piqued my interest a bit. Here is a pretty good discussion, Adding Acid Via The Skimmer

Great find!! Sums up exactly all of the technical problems with chemical additions through a skimmer.

bobdenny2,

You've been given the very best advice possible with relation to adding chemicals to a skimmer. It's the same advice we give everyone - don't do it.

If you choose to ignore that advice, that is certainly your prerogative. It's your pool and your pool equipment to do with as you please. Adding acid slowly to the deep end and brushing with a wall brush while the floor jets are running will be more than adequate to mix the acid up. The small amount of extra time saved by not doing it that way does not seem to be worth damaged motor seals or a ruined heater core to me but your cost/benefit/time calculation may be different.

Good luck to you,
Matt

 

[BobDenny2]

The forum is slow tonight and this piqued my interest a bit. Here is a pretty good discussion, Adding Acid Via The Skimmer

That forum was exactly what started me on this exploration. From the posts, they essentially concluded that there was no empirical evidence that adding MA to the skimmer actually causes harm, and they said some experiments would help clarify the matter.

One of the final posters (Valera) even describes putting very large quantities of acid into the skimmer-20 Liters in 20 seconds!—on pools used to test equipment.

 

[pooldv]

Except for this post from one of the forum founders.

Begin quote
Getting back on topic...
The biggest dangers from pouring acid into the skimmer (or putting trichlor in the skimmer) are to the pump seals and to filter cartridges if you have a cartridge filter. IMHO, you can ruin the cart faster than the seals but both will suffer damage in not that long a time if the process is a regular one.
Damage to pump seals is obvious, they start to leak but the damage to carts actually can take on two different appearances.
The obvious one is the degredation of the rubber end caps on the cart. They get gummy and can actually start to 'dissolve' and leave a residue throughout the system and plumbing. I experiened this one first hand when my pool was being built (thanks to an idiot pool builder who is now out of business) and I actually had to wipe out residue from the dissolved end caps from my skimmer! (Not to mention the mess it made inside my filter chamber!)
The second type of damage is a bit harder to spot but the usual symptom is that your filter pressure increases rapidly after freshly cleaning the cart. The reason for this is exactly the same reason that you do NOT want to acid wash a cart until you have degreased it first. The acid hardens the organics that collect on the cart into a cement like mass that effectivly ruins the cart and requires it to need replacement. This is documented on both the*Unicel Filters*and the*Pleatco*websites in their sections on proper cleaning of carts, btw.*

Also, continued expose to acid will cause the polyester material the cart is made of to stretch and actually lessen it's filtering ability. This is why it is recommended to only acid wash a cart when it is needed (scale deposits are present after soaking n a degreaser).

Bottom line is this, pouring acid into your skimmer is risky at best and downright dangerours at worst!

Hope this info is useful.

end quote

 

[BobDenny2]

Great find!! Sums up exactly all of the technical problems with chemical additions through a skimmer.

bobdenny2,

You've been given the very best advice possible with relation to adding chemicals to a skimmer. It's the same advice we give everyone - don't do it.

If you choose to ignore that advice, that is certainly your prerogative. It's your pool and your pool equipment to do with as you please. Adding acid slowly to the deep end and brushing with a wall brush while the floor jets are running will be more than adequate to mix the acid up. The small amount of extra time saved by not doing it that way does not seem to be worth damaged motor seals or a ruined heater core to me but your cost/benefit/time calculation may be different.

Good luck to you,
Matt

Surprise is (really) a city in the northwest valley of the Phoenix metro area, population about 125,000

So I’d just like to reiterate: I do not propose anyone do what I do. As you say, your pool, your prerogative.

But with all due respect, just saying “don’t do this because we think it is bad” without any empirical evidence is not a very satisfying answer to me. I understand that, theoretically, bad things could happen based on the chemistry. But theory and reality don’t always match.

The 2007 thread participants suggested that the most likely failures would be:
1) Heat Exchanger
2) Pump and Filter Seals
3) Cartridge media

Perhaps folks here have a different perspective?

I intend to test the seals next because I feel that the amount of damage done to the heat exchanger is at best minimal, and unlikely to measurably change the heater’s usual lifespan of ten years.

As I pointed out in my first post (and the 2007 thread also discusses): Pouring MA into the skimmer for 15 seconds, once per week, for 10 years adds up to about 2 hours of total exposure to Diluted MA. If this was truly damaging I would think that we could demonstrate that fairly quickly with a few real-world experiments

 

[pooldv]

So, if there is potential, however small, for damage by adding to the skimmer and much less, or no, potential for damage by adding it to the pool with the pump running why wouldn't we recommend that and advise against adding it to the skimmer?

Interesting, Surprise is kind of a funny name for a city. I was quite amused by that location.

 

[BobDenny2]

So, if there is potential, however small, for damage by adding to the skimmer and much less, or no, potential for damage by adding it to the pool with the pump running why wouldn't we recommend that and advise against adding it to the skimmer?

Interesting, Surprise is kind of a funny name for a city. I was quite amused by that location.

The local legend is that the woman who owned the land when she founded the city called it Surprise because she would be surprised if anyone ever moved here. I think that was in the 1930’s

I fully concede your point on “some potential risk” of adding to skimmer versus “small potential risk” of diluting and adding near an active pop-up. Adding acid anywhere appears to carry some risk (pooling). I am simply curious about the “actual” risk, and personally find it far more convenient to add to the skimmer than other methods.

I’m performing these experiments essentially to convince myself, one way or the other, of the actual risk. I’m sharing them here in case others might find it interesting or valuable, but am not advocating anything.

 

[AUSpool]

All of the reasons not to are related directly to potential equipment damage but what of a biological effect? The effect of a strong acid on all the debris or biological matter captured in the filter and the potential to send it back out into the pool as the plume of dust that I noticed when I did it once. Is it possible to create suspended solids that are too small to be captured by the filter, particals that could settle out of the water but would be re-suspended every time the pool is used again.

 

[BobDenny2]

The local legend is that the woman who owned the land when she founded the city called it Surprise because she would be surprised if anyone ever moved here. I think that was in the 1930’s

I fully concede your point on “some potential risk” of adding to skimmer versus “small potential risk” of diluting and adding near an active pop-up. Adding acid anywhere appears to carry some risk (pooling). I am simply curious about the “actual” risk, and personally find it far more convenient to add to the skimmer than other methods.

I’m performing these experiments essentially to convince myself, one way or the other, of the actual risk. I’m sharing them here in case others might find it interesting or valuable, but am not advocating anything.

So now over 2 years adding MA to my skimmer on a weekly basis. No issues, no damage, no leaks.

I haven’t yet found an easy way to directly test a pump seal. I thought about just purchasing a replacement seal and soaking it in MA and hydrogen peroxide, but I don’t have a good way to test whether it would actually be leaking after that test. I guess my current pump is the test subject. Still no leaks

But I found a separate bit of information that seems to support that the MA will not materially damage cartridge filters.
This is a direct quote from the Hayward user manual for my 8 cartridge pool filter: “Cleaning Cartridges: If calcium or mineral deposits are excessive, the cartridges may be restored to “like new” condition by soaking in muriatic acid. Use commercially available 20% muriatic acid added to water in a 1 to 1 ratio.”

Look, I know Hayward has a commercial interest in selling more cartridges, but if this procedure actually damaged the cartridges I think they would find themselves in hot water for recommending and saying it makes them “like new.”

I saw another post about oils and cleaning solutions clogging a filter cleaned with MA. I understand the potential for problems, but my real world experience simply does not substantiate this. I actually replaced the 8 cartridges a few weeks ago, just because they were in the filter when I bought the house and I could not tell how old they were. The straps were breaking off, but otherwise the filters were working fine.
There was no pressure change from the old filters to the brand new ones, i.e. both sets show the same pressure differential while the pump is running at full speed. So the really old filters withstood almost 2 years of my MA abuse and did not clog. There was also no sign of anything degrading the plastic end caps.

My usual caveat: I’m not suggesting anyone add MA to their skimmer. I do so because it is most convenient for me with my pool configuration. There is clear hypothetical potential for damage, but I also cannot verify that ANY of the potential damage of doing so is real. I’m only sharing this information in case other forum members are interested

 

[pooldv]

Thanks for the update. We also recommend cleaning filter cartridges with diluted muriatic acid if there is any mineral build up here, Re: How to clean a cartridge filter

That is probably where you also saw the warning to clean with TSP first:

WARNING: Failure to remove all oils and cleaning solution before acid soaking will result in a permanent restriction of water flow and cause premature cartridge failure.

My caveat is that there is no benefit to adding MA to the skimmer so why risk it? And it is easier to float the MA bottle in the pool so that the mouth of the bottle is only an inch above the water to pour it. This virtually eliminates any potential for splash.

 

[BobDenny2]

Thanks for the update. We also recommend cleaning filter cartridges with diluted muriatic acid if there is any mineral build up, here Re: How to clean a cartridge filter

That is probably where you also saw the warning to clean with TSP first:

WARNING: Failure to remove all oils and cleaning solution before acid soaking will result in a permanent restriction of water flow and cause premature cartridge failure.

My caveat is that there is no benefit to adding MA to the skimmer so why risk it? And it is easier to float the MA bottle in the pool so that the mouth of the bottle is only an inch above the water to pour it. This virtually eliminates any potential for splash.

Thanks pooldv, might be nice to know your name? Or should I just call you TFP?

Yes I did see that post, and I probably didn't articulate it very well, but my point was that I have NEVER used TSP, and assuming there were some oils etc. from my swimmers, wouldn't it stand to reason that pouring MA in my skimmer would have caused the clogging the post describes? In two years I never once used anything except clear water to rinse my cartridges, and I've poured MA in my skimmer every week, yet there was not a measureable change in flow from those cartridges to the brand new ones. Maybe my swimmers aren't as oily as everyone else?

As for the benefit, my pool doesn't have normal returns, only in-floor pop-ups. I can of course stand in one corner until the pop-up controller gets to me, but it is still 4 feet below the surface, and only remains in that position about 20 seconds before moving to the next zone. So unless I chase it, I'm going to end up with acid pooling somewhere. Yes I know I should then brush. I'm sure everyone on this forum but me brushes constantly

As I said above, my configuration makes using the skimmer vastly more convenient, and it also does a really great job of prevent pooling of acid by distributing it everywhere in the pool.

Unless and until I'm convinced there is ACTUAL, not just potential damage, I'm sticking with the skimmer

 

[pooldv]

LOL! Yep all good TFPers brush like they're supposed to. I changed our autocorrected TFPs to TSPs. Trisodium Phosphate is what should be used to clean filter cartridges first time.

My guess is that the MA is diluted enough by the time it gets to the cartridge. The real point in the cartridge cleaning tutorial is not to soak the cartridges in MA before cleaning with TSP. I mostly just hose mine off also, I've used TSP a couple of times and it seems to help a bit. I've never soaked them in diluted muriatic acid.

You can call me bacon man or Danny.

 

[BobDenny2]

LOL! Yep all good TFPers brush like they're supposed to. I changed our autocorrected TFPs to TSPs. Trisodium Phosphate is what should be used to clean filter cartridges first time.

My guess is that the MA is diluted enough by the time it gets to the cartridge. The real point in the cartridge cleaning tutorial is not to soak the cartridges in MA before cleaning with TSP. I mostly just hose mine off also, I've used TSP a couple of times and it seems to help a bit. I've never soaked them in diluted muriatic acid.

You can call me bacon man or Danny.

Bacon Man?? Best nickname ever! Everything is better with bacon!

I don't know if you read some of the prior posts on this thread, or the 2007 thread with the same topic. But the recurring theme is that everyone thinks adding MA to the skimmer is bad, yet no one seems to have any evidence of actual damage. As I said on one post, the answers seem to be "we think it's bad so don't do it" without any true evidence. I'm not trying to be a troublemaker, I just want to know what is real and what is just unfounded fear. Yes it's acid and can destroy stuff. So is lemon juice

Maybe no one else cares or is willing to risk their equipment for what is a slight inconvenience for them, and I get that. For me the inconvenience is larger, and yes I'm willing to risk a pump seal to find out if I'm right. I think my logic around total exposure is actually sound, and the test with the copper suggests heaters are not really all that at risk. So yes I'm also willing to risk my pool heater. Obviously others will not share my risk tolerance, but I hope we can continue an open conversation about this