# Lowering KH (alkalinity) using muriatic acid, a venturi, and a trash can



## TWood (Dec 9, 2004)

Using muriatic acid to lower alkalinity (KH) is described in a swimming pool forum thread located HERE. So it's not my own, I've just adapted it to aquariums. Aerating the water is key to the method, it's NOT just adding acid.

Our tapwater starts at 15dKH. After experimenting with the method, I found that 5ml muriatic acid will lower the KH of 35 gallons of water about 1dKH. One of you chemists can step in any time and calculate the exact amount, if possible, and maybe come up with an easier ratio to work with. So to get 35 gallons of 15dKH water down to near-zero KH took about 75ml of muriatic acid. YMMV, so dose lower and test frequently, this isn't something you want to overshoot.

I placed a submersible pump in a garbage can containing 35 gallons of water, and used a venturi to aerate the water:










You can also use a short hose and redirect it back into the water so it churns and makes bubbles. Basically you just measure the starting pH, add the acid, let it aerate for a while, then measure the pH again. When the pH comes back up, measure the KH - it will be lower. Repeat until you have the KH where you want it. If you overshoot with the acid, both pH and KH will be off the bottom of the test kit measuring ability. So it's best to do a little at a time so you can at least -get- a measurement.

It took a couple of hours to get the KH down, which meant that pump was in the water running that long, which raised the temperature of the water. So plan on letting it sit and cool off after this is done. Also, be -very- careful handling muriatic acid. That's a little skull and crossbones on the jug label - for good reason. It lets off fumes so be upwind and outside when pouring it. I used a graduated cylinder to measure.

From 15dKH I now have it down to less than 1. See THIS THREAD for why it may be better to get it this low.

If you use an electronic meter to measure TDS, it will go up. See discussion HERE for what the TDS change really is.


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## milalic (Aug 26, 2005)

I always had the idea if you used muriatric acid your TDS will be going down because it eats KH and gh. Have you measure the ph of this water?What about the salt contents over time, it might affect plants if the link you provided above is correct.

-Pedro


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## TWood (Dec 9, 2004)

If you use just the right amount of acid, the pH ends up where it started. 

The salt might be an issue over time, but I use RO for evaporation replacement mostly to avoid GH buildup from our 23dGH tapwater. I have a 90 gallon tank, and making that much RO water on a low-pressure rural water system is a pain, hence using this method.


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## milalic (Aug 26, 2005)

The uses I have seen before is to lower ph by eating gh and kh.
So not sure how the ph will stay the same if you are adding acids. 


-Pedro


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## TWood (Dec 9, 2004)

Read through the process, the aeration removes alkalinity in the form of CO2, raising the pH back up.


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## Salt (Apr 5, 2005)

HCl will lower KH by turning CO3 into CO2, but it will also raise TDS by adding chloride ions.

A better choice for planted tanks would be a bisulfate like KHSO4 or NaHSO4, which does the same thing, but adds sulfate ions as the by product. It can also work by simply dissolving in water and adding it directly to the aquarium.

Seachem's Acid Buffer product is primarily NaHSO4.


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## DataGuru (Mar 11, 2005)

So what concentration is your muriatic acid?


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