# Lower KH by Using Pool Acid to Achieve "Soft Water"?



## cS (Jan 27, 2004)

Any reason why we can't use HCl (muriatic acid, pool acid, etc.) to lower the KH in our water?

I personally have very soft tap water but I keep reading about people wanting to use RO water to have this mystical "soft water" because theirs is hard. And then I read that several "experts" contend that "soft water plants" prefer *LOW KH* and *not* low GH. Therefore, is there any reason why we can't use some strong acid such as HCl to destroy the carbonates in order to lower KH but keep GH the same? Would this work? What sort of danger should I expect?

If it works with minimal dangerous side effects, then folks with hard water can simply use this method instead of investing in the relatively costly/cumbersome RO water method.

What do you think? Just curious. :noidea:


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## plantbrain (Jan 23, 2004)

Oh yea, sure, about 10 years ago folks tried all sorts of whacky things. Adding strong acids to destroy KH was one such foolish attempt.

Use an RO, much safer, less mess, less toxic, more productive.
I can promise you will spill some on you and you will cut corners and the transfer will get you. Maybe not today, but at sometime in the future unless you are extremely careful.
Acid burns suck.

RO?
No such issues and RO's can be had for cheap on ebay etc.

Handle strong acids is not a thing I would suggest for hobbyists.
Simply blend the RO with tap to achieve a good KH, top off any GH as needed.

Regards, 
Tom Barr


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## cS (Jan 27, 2004)

Thank you for chiming in Tom. If I read you correctly, then you are saying that a strong acid such as HCl *will* lower KH ... but it's a dangerous chemical to handle. It's good to know that it works.  I am sure the ingenuity of hobbyists will come up with some safety precautionary measures.



plantbrain said:


> Use an RO, much safer, less mess, less toxic, more productive.


Safer and less toxic I would agree. But "less mess" and "more productive" I would respectfully disagree. Employing a strong acid such as HCl would simply involve adding it directly to the aquarium/sump or to pretreated water in some container. If not less messy than it rivals that of a RO unit. Furthermore, such a unit produces comparatively a lot of "waste" water. HCl does not. There's nothing to discard. Couldn't be easier and very inexpensive.

Safety is of course a very real concern. Is there any reason why we can't dilute it to make it safer? Pool acid is sold over-the-counter to pool owners. How do they handle it?


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## MoonFish (Feb 12, 2006)

tom is smart. i'm sure he has done this before. if he says it is a bad idea and you don't believe him it is just because he hasn't recited his encyclopedia of knowledge to you. 

back to the subject, if it was that easy to do then cities would just add acid to the water and send it right to your house but they don't. just google "alter ph acid" or something similar. in my quick google trip i got a summary in my head that amounts to something like the acid basically kills the alkalinity before it affects the ph then suddenly the kh is gone and the ph drops bigtime and the results aren't that predictable but maybe i am summarizing too heavily or i got off the path somewhere. 

but i haven't lifted a finger on the subject so you can show me pics of your acid injected aquarium when you make it work.


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## BryceM (Nov 6, 2005)

Yep, it will chew up your buffering potential and lower pH at the same time. The downside is that a little will go a LONG way. You could easily dilute it to a concentration that would be less dangerous to handle, dispense, etc. The trick is that you'd need to test very carefully to avoid an overdose. A small amount of HCl will drop the pH VERY quickly once the buffer is used up. You'll also be raising the chloride ion concentration - probably not a big deal up to a point.....

The other problem is that water that is naturaly hard got that way by passing over soluble materials on its way to your tap. This tends to add calcium, magnesium, carbonates and a variety of other salts depending on where you live. Most natural water has either a high GH & KH or a low GH & KH. Artificially lowering one will result in a situation not often seen in natural water. Using an RO unit will lower all of the various dissolved solids at the same time. Will HCl work? Maybe, but it's really not worth the trouble most of the time.

HCl + NaHCO3 --> 2H2O + NaCl + CO2

BTW, cities don't mess with buffering capacity for several reasons. #1 - Why bother? They might be interested in lowering the general hardness (GH), but nobody but us cares about the KH. #2 - it's expensive, #3 - lowering the pH by doing this would speed up corrosion in the pipes = big expenses to replace main lines.


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## titan97 (Feb 14, 2005)

As a pool owner and chemist, I can comment that handling HCl isn't that big of a deal if you are careful. With that being said, I'm also adding 1 liter to a 13,000 gallon pool, so I don't have to worry about very small (mL scale)additions. I can slop it around and not worry about it. However, if I chew through my alkalinity, I can and will ruin the plaster pool walls and any non-plastic plumbing. Having a pool is just as demanding as having an planted aquarium.

Anyway, I've always understood that KH isn't as big of a deal as GH is. I could be wrong on this, but I grow weeds like crazy in a very high GH/KH (25 degrees GH/15 degrees KH) tank.

-Dustin


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## jude_uc (Feb 7, 2006)

As a former maintainer of pool, I can also say that HCl has very strong fumes... If you bend over it as you pour, it will make your eyes and lungs very unhappy. The main problem is that HCl is one of the 'strong acids', so small amounts make a big difference. Also, the stuff sold for pools is decently concentrated. I would stay away from it if possible. Finally, commercially made 'ph-down' is often dilute H2SO4, one of the other 'strong acids'. It does eat through buffering capacity until it starts to change your pH; however, the key is that it is very dilute. Strong acids at any reasonable concentration shouldn't really be messed with. 

-Adam


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## MoonFish (Feb 12, 2006)

yeah was reading a bit. check out the msds sheet for this one http://www.growthtechnology.com/msds-phdown.asp

i get the idea if you had extra barrels of water and an affinity for test kits you could do it. but lots of people have done it already. if you google "ph crash" you can read their stories.


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## plantbrain (Jan 23, 2004)

Well you folks go on and try adding it to your tanks and see how things turn out, but do not say I did not tell you so, pools and public tap water are a total different critters.

I've used it and any strong acid will rip the bicarb apart releasing the OH and the CO2.

You can read some of the APD post and then figure out why it never became a popular idea. 

The main issues with liquids: easy to spill, transfer is where most accidents occur, controlling the level of KH removal, death to critters in the tank.

RO is a much wiser idea and method.


Regards, 
Tom Barr


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## cS (Jan 27, 2004)

Thank you so much for all your input guys. I hope that I am able to adequately respond to each point. :fear:

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:laser: _*The acid will destroy alkalinity.*_
Yes, and that is exactly what we want: to lower KH. A RO unit lowers KH by removing carbonates through filtration. Acid lowers KH by destroying the carbonates. There is no net difference between either methods.

H+ + HCO3- --> H2CO3 --> CO2 + H2O

In fact, with the acid, one can control how much HCO3- is removed by varying how much of the acid you add. With a RO unit, you have no choice but remove _all_ of the HCO3- and then add the carbonates back.

:icon_hang _*You will get a pH crash when the KH is all used up.*_
This I feel is blown out of proportions. Remember that RO water has no KH and so the addition of _any_ acid, including carbonic acid that will inevitably form from the addition of CO2, can cause wide pH swings. This "problem" is certainly not unique to water treated with an acid; so you are not exempted from this phenomenon if you use RO water.

But that is irrelevant because we are not aiming for 0 KH. RO water users mix their 0 KH water with tap water or add NaHCO3/CaCO3/etc. to bring back KH. Likewise, acid users will also need to bring back the KH _if and only if_ they overdose the acid because...

...we only need to use enough acid to lower the KH by a specific number just like we add enough KNO3 to raise [NO3] by 10 ppm. I am sure a formula can be derived to tell us how much acid to add in order to reduce KH by X degree. You can lower KH 0 degree, 3 degrees, 10 degrees, etc.  We have fairly precise control over that.

A KH testkit would be helpful but not necessary since the relationship is fairly straightforward: adding X amount of acid will lower KH by X degree. And if you need one, then use the one you already have for the RO water application. This is certainly not an extra cost.

End GH Discrimination. We Demand EQUAL RIGHTS._*The acid only lowers KH whereas the RO unit will remove both KH and GH, along with other solutes.*_
The fact that the acid does not remove GH (Ca/Mg) is a good thing. Ca and Mg are nutrients; and I have not read anyone contending that high Ca/Mg is detrimental to plant growth, including those plants that are designated as "soft water plants" (i.e. the _Tonina spp._). The issue, many believed, is high KH. Please correct me if I am wrong here. Therefore, the lowering of KH but keeping GH the same should be a perk instead of an unfavorable consequence.

With regards to the "other solutes", I must concede that it might be a legitimate concern; although I am not certain what these "other solutes" are or how they can be detrimental to plant growth. Someone would have to clarify this for me.

ainkille _*Safety. Many strong acids are sold as concentrated solutions and are not safe to handle.*_ 
I will admit that this is indeed an issue. But there are alternatives and precautions that can be taken to make these strong acids safe to use. After all, many of these acids can found in pH-Down products within our hobby such as H2PO4 and H2SO4. H2PO4 is particularly advised against not because it is dangerous but because it interferes with the pH/KH/CO2 table. H2SO4 (probably originating from NaHSO4) is found in Seachem's Acid Buffer (powder or liquid forms) which is safe for use with planted tanks. Certainly, we can make dilute solutions of these acids or deal only with the dry forms. Both of which can be purchased from the pool supply stores.

Muriatic acid (HCl) has long been recommended for use to test if a rock is "safe" for aquarium use. But the commercial HCl may be too acerbic and volatile to be handled. However, we have other safer alternatives such as the H2SO4 ph-Down that jude_uc mentioned. So even though safety is an issue, it _can be_ remedied.

---

Are there any other problems that you could think of? Have I adequately and fairly rebutted all the problems raised? Have I left any issue unanswered? :boink:



> I've always understood that KH isn't as big of a deal as GH is. I could be wrong on this, but I grow weeds like crazy in a very high GH/KH (25 degrees GH/15 degrees KH) tank.


That is very true. Your tank and Travis Simonson's tank (the gentleman with the mbuna planted tank) certainly attest to that. However, what I am proposing is an alternative to a RO machine for those who, for one reason or another, desire softer water. Furthermore, some experts insist that "soft water plants" such as the _Tonina spp._ prefer low KH. Whether or not that is true, I can't say.



plantbrain said:


> You can read some of the APD post and then figure out why it never became a popular idea.


Tom, it's not that I am lazy but I am unable to find anything in those old APD posts aside from the "problems" already raised by others in the above posts.  And these problems were never rebutted. Or perhaps I am unable to find those rebuttal postings? I searched for "HCL" and "RO" as well as "lower KH". Furthermore, much of the discussion had been about HCl instead of the other acids. The only non-HCl acid mentioned was H2PO4 and those discussions were confined to the pH/KH/CO2 table which is irrelevant to our discussion. And some postings about H2SO4 but again those were used to achieve some mythical "perfect pH" which is not what we are aiming for and so the conclusion of "should not be using it" does not apply to our discussion here.

Safety has already been addressed above. Would you point me to the discussions that you are specifically referring to? After all, HCl is not the only choice and there's a myriad of pH-down products available that destroy bi/carbonates using H2SO4, H2PO4, etc. Are they also as *dangerous* as people are making it to be? I am very doubtful but am open to being proven incorrect.  After all, the concept is essentially the same.



Moonfish said:


> if he says it is a bad idea and you don't believe him it is just because he hasn't recited his encyclopedia of knowledge to you.


I am in fact counting on it because I honestly do not understand why it is so advised against. :mrgreen: Is it because I chose muriatic acid as an example instead of Seachem's Acid Buffer?


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## BryceM (Nov 6, 2005)

Go ahead. Try it. I'd love to hear how it goes. I'm sure if you're careful it will work ok. Bottom line for me:

Ability to have inadvertent fish kills with pressurized CO2 - it can happen.
Ability to have inadvertent fish kills with RO water - unlikely.
Ability to have inadvertent fish kills with HCl - absolutely.

Just one more thing that _could_ go wrong. I have enough to worry about already. Also, many people that use RO do it because their tap water is too high in NO3, or PO4, or NaCl, or one of a hundred other things. Good luck.


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## MatPat (Mar 22, 2004)

I too am interested in the results. My KH is made up of who knows what and the pH/KH chart is already invalid in my case due to a phosphate buffer added to my tap water. I have an RO unit, but am getting tired of making and wasting so much water each week. 

I'd love to be able to add a minute amount of HCL, (I have a gallon for the pool and I agree with titan's observations on the pool) to lower my KH a bit. Since my chemistry knowledge is fairly low (long time since high school) I'd have to go about this by trial and error. I could always experiment with an old 10g tank and some feeder guppies


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## Blazerfrs (Feb 3, 2006)

I can't even dose 1.25 ml of excell without spiling it all over myself and my desk- I can't imagine trying to add Hydrochloric acid to my tank. 

Listen to Mr. Barr. He knows his stuff.


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## plantbrain (Jan 23, 2004)

Oh it does work, but it takes awhile, you need to be careful, some clown will not and then we will hear about it later, I'm sure. Yellow spots all over their arm

Folks used peat also.
Now why not use peat?

It's rather hard to hit a known amount each time.

Also, the APD post, look at that.

The issue is that when you add strong acids, they are foul smelling, they require another container to mix the water in, it works, I'm not saying it does not, I just think RO is simpler for most folks and so do most folks that have used things like HCL and H2SO4 like I have.

The KH was difficult to adjust.

A pool etc where you do not do regular water changes, this is one thing, you want to kill bacteria, algae, plants etc, then let it settle down and the volume involved is much larger, RO is not practical for that, I'd personally do partial lime softening for a pool, it's the GH that's the issue there.

When you do softening with acids or lime for Ca++, there is a lot of OH's floating around.

These are nasty. Premix the water, never add directly to your tank.
I know someone is going to kill their fish.

We have certain similar topics pop up every 1-2 years or so.
And the vicious cycle repeats.

I do try and steer folks in a good direction but I do also reserve the poster's specific issues/situation and trade offs they are willing to deal with.

If I suggest it for CS, many end up thinking it applies to them, when in fact, it very well may not. Don't be harsh on CS, asking legit questions that have been hashed over years ago, sometimes needs the new cohort to see and discuss it also. Then when 5 years from now, a newbie comes along and ask, you'll be able to help.

I think for a few eclectic plants, it's not worth messing with this, if the plants are that big of an issue, use the RO, you can use it for drinking water also, reef tanks etc. It's easy to, turn water on, wait for the vat to fill up, use and blend with Tap to get the right KH.

Buy some ADA aqua soil, since CS is also a vendor of weeds, this would be a wise idea, I'd not use the powersand though, but some are stubborn, I have a trick for that in a sales grow out tank if you must use that so that it stays put.

Regards, 
Tom Barr


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## cS (Jan 27, 2004)

plantbrain said:


> since CS is also a vendor of weeds


You are confusing me with Charley S. (Lowcoaster) of Aquabid. I am *not* him.

As far as the rest, I'll need to do some research and consult a few experts before I can formulate an adequate (read: _short_) response. :mrgreen:


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## plantbrain (Jan 23, 2004)

cS said:


> You are confusing me with Charley S. (Lowcoaster) of Aquabid. I am *not* him.
> 
> As far as the rest, I'll need to do some research and consult a few experts before I can formulate an adequate (read: _short_) response. :mrgreen:


Are you sure? hahaha, anyway, sorry there........did not mean to confuse you with Charley........

regards, 
Tom Barr


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## Edward (May 25, 2004)

Hi
Not sure if the HCl will work for plants, but definitely not for the fish. The conductivity will jump astronomically with the acid. Fish will go into shock. This is like using a salt regenerated water softener that removes hardness and calling it an equivalent of RO water. This is not going to work.
RO units today are cheap, reliable and very economical in the long run. Adjust the waste water to lower ratio if you are concerned about the cost of cold water. Also the clean water is going to keep you healthier if you use it for drinking and cooking and the waste water can be used for plants and aquariums running non-RO water. RO water running aquariums are exciting.


Edward


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## TWood (Dec 9, 2004)

We recently bought a house with a pool in a location with very hard water also high in alkalinity. Nothing worked for the plants until I used adjusted pool water in the tank.

There is a method for lowering alkalinity using muriatic acid that does work. But it's not just adding acid. It involves lowering the pH -a little- with acid, then aerating the water until the pH rises, then lowering the pH again (and again and again) using acid, then aerating the water until the alkalinity drops to where you want it. The method and the reasoning behind it is described HERE.

I tried RO and it's way too much trouble compared to this. Rather than adjusting the alkalinity in the tank, or using a pool, just do it in a large plastic garbage can before adding the water to the tank.

TW


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## DataGuru (Mar 11, 2005)

The best reference I've found on using muratic acid for reducing KH is Roark's site. You have to register to get to it, but he covers in great detail safety and how to do it including the concentrations and dosing. See the section under water quality called "lowering KH".


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## banderbe (Nov 17, 2005)

I love my RO unit. Single best purchase I've ever made for this hobby.

The notion that RO is somehow inconvenient is totally absurd. I find RO easier to use than tap water.

The RO unit connects to a float valve and an auto-shut off valve and runs into a 32 gallon rubbermaid trashcan, and in the can is an 800 gph pump with a hose attached. To fill my tank I just screw on a hose, plug in the pump and away I go. When the water level drops the RO unit fills it back up. Way easier than trying to screw a hose onto my sink faucet. Additionally, I can now create any water chemistry in the world for any fish or plant. The possibilities for my hobby are now limitless, or at least no longer limited by my water. Breeding fish? No problem. Growing tonina? Piece of cake. Well, okay not a piece of cake but you get my point! An RO unit is a great investment and I wouldn't trade it for anything.


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## banderbe (Nov 17, 2005)

By the way folks, I'll take this opportunity to plug for my favorite RO retailer. If you want an RO unit, you cannot go wrong with these guys.

http://www.abundantflowwater.com

Their 100GPD Reef Master RO/DI unit is $175 and worth every penny. Customer service is _outstanding_.


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## DJKronik57 (Apr 17, 2006)

> The notion that RO is somehow inconvenient is totally absurd. I find RO easier to use than tap water.


What is convenient to one person may not be convenient to another, calling their opinions absurd is a little harsh as well. As an example, I don't have room anywhere for a 32 gallon trashcan, can't even afford pressurized CO2, and the thought of figuring out plumbing and valves brings images of my apartment flooded to my mind! Some of us who like DIY projects have an entirely different notion of "convenient" anyway! Getting it done yourself, no matter how inconvenient, is sometimes a bit more fun and rewarding. I think the attraction to using an acid versus RO water is that it would be simply adding a few drops to a water mix instead of having an entire installed (and expensive) system devoted to making water. However, I think we can safely say that using acid would probably be just about as complex and troublesome as an RO unit, not to mention dangerous.

As always in life, there's the less-risky, expensive way, and then there's the hasty, cheap-but-full-of-dangers way. It all boils down to how much of a risk you want to take.


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## Edward (May 25, 2004)

Tonina is difficult? No way, it grows like weed in RO water and inert substrate. 
If your tap doesn't grow your plants then RO is the right option. Acid won't work.


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## Edward (May 25, 2004)

Here is an example what *RO* and inert substrate does to Tonina with PPS fertilization I grow for testing. 
It's a weed &#8230; growing out of control.


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## Jason Baliban (Feb 21, 2005)

What is your fert method for that tank? Oh, and your CO2 method?

Thanks Edward.

jB


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## hoppycalif (Apr 7, 2005)

Jason Baliban said:


> What is your fert method for that tank? Oh, and your CO2 method?
> 
> Thanks Edward.
> 
> jB


You can be sure when Edward is posting he is using PPS! Of course he also said he was using PPS, so that's two bits of evidence. There is more than one way to grow aquatic plants well.


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## Edward (May 25, 2004)

No Acid
RO only, 100%
NO3, 10 ppm, (PPS)
PO4, 1 ppm, (PPS)
K, 13 ppm, (PPS)
Mg, 2 ppm, (PPS)
Ca 15 ppm, (CaCl2)
dKH 0.3 (baking soda)
CO2, 20 ppm, 24/7
pH, 5.65, (the lowest pH, CO2 can do)
50 gallon
120 W, PC in reflectors, 10 hours
2.4 Wpg
TE mix, 0.3 ppm Fe 
CaCO3 and MgCO3, zero
32 C, 90 F
TDS 160 uS micro Siemens
Eheim pump 1250
CO2 manual needle valve, pressurized
Aqua Medic CO2 Reactor 1000
inert substrate silica sand 

_Nymphaea lotus (zenkeri) 'Red'_ 
and

_Tonina sp. 'Manaus'_
or
_Tonina sp. 'Belem'_


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## Jason Baliban (Feb 21, 2005)

Thanks Edward!!

PPS rocks!!

jB


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## BryceM (Nov 6, 2005)

90 deg F!!!! The toninas might be doing ok, but not everything would......


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## Edward (May 25, 2004)

It's the summer house temperature, I can't help it.


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## hoppycalif (Apr 7, 2005)

A tiny little fan blowing across the water surface will cool the water at least 5 degrees F. The trade off is that it evaporates more of the water to do the cooling. But, with your RO water at least that won't affect the hardness.


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## Patchworks (Dec 20, 2008)

Did anyone ever test this idea? I have high KH and this concept seems like a DIY solution I would prefer. Especially after reading the article at Roarks Website Posted in this thread!! Very good info...

g


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