# Diluting tapwater with distilled water



## Ami (May 27, 2011)

Hi,
I was wondering how to add tap water that has been diluted with distilled water to get a desired hardness and pH - specifically, can you add the distilled water straight and then add tapwater? Or is it better to let the waters mix, let it stand for a while and then add it. 

Thanks,
Ami


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## brokenrules69 (Aug 27, 2011)

if u are trying to make ur hardness lower i don't think distilled water will help
im pretty sure u need reverse osmosis water (RO) or pure H20
or rain water is basically the biggest cheapest RO filter ever as long as u don't live near a city 


but what i usually do is mix half and half in a 5gallon bucket while doing a 20% water change and then pour in very slowly but making sure the water is right temp first


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## Byron (Mar 7, 2009)

Distilled water will work, same as RO or rainwater. In all cases, adding the "pure" weater will dilute the tap water proportionally, example half tap water and half pure will result in the hardness being half of what the tap water is. This should not be done in a tank with fish, but either in pails or in a fishless tank. Test the water for hardness and pH. Recognize that the hardness will remain at whatever level it is after the mix, but the pH will lower as the biology of the tank becomes established. Of course, this means fish should be in the tank once the water is mixed and stable.

If you need to use pails and then add the water to an existing tank such as with a partial water change, do it slowly, depending upon the initial hardness and where you want it to end up. A partial water change of 1/4 may be all, or 1/3, and each carried out weekly, or more often; it depends upon the hardness.

Byron.


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## SinCrisis (Aug 7, 2008)

Note that distilled water is pure and can cause the PH of the tank to be less stable since there are fewer buffers in distilled water.


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## Ami (May 27, 2011)

Byron said:


> Distilled water will work, same as RO or rainwater. In all cases, adding the "pure" weater will dilute the tap water proportionally, example half tap water and half pure will result in the hardness being half of what the tap water is. This should not be done in a tank with fish, but either in pails or in a fishless tank. Test the water for hardness and pH. Recognize that the hardness will remain at whatever level it is after the mix, but the pH will lower as the biology of the tank becomes established. Of course, this means fish should be in the tank once the water is mixed and stable.
> 
> If you need to use pails and then add the water to an existing tank such as with a partial water change, do it slowly, depending upon the initial hardness and where you want it to end up. A partial water change of 1/4 may be all, or 1/3, and each carried out weekly, or more often; it depends upon the hardness.
> 
> Byron.


 Thanks. Now I know what I was doing wrong ! When I was trying to lower the hardness from 300 ppm to 75ppm in my aquarium I was adding the disitilled water directly. That might explain why my fishies, especially the glowlight tetras were dying :-( My hardness is currently between 75ppm and 150ppm. How can I lower the hardness without adding distilled water directly? Shuold I dilute it with aquarium water to the desired hardness and then add it back to the aquarium (all of this will be done during water change of course).

Aquarium details are at 
55 gallon community - 55 gallon Freshwater fish tank


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## Byron (Mar 7, 2009)

Ami said:


> Thanks. Now I know what I was doing wrong ! When I was trying to lower the hardness from 300 ppm to 75ppm in my aquarium I was adding the disitilled water directly. That might explain why my fishies, especially the glowlight tetras were dying :-( My hardness is currently between 75ppm and 150ppm. How can I lower the hardness without adding distilled water directly? Shuold I dilute it with aquarium water to the desired hardness and then add it back to the aquarium (all of this will be done during water change of course).
> 
> Aquarium details are at
> 55 gallon community - 55 gallon Freshwater fish tank


With fish in the tank, the best method is to do the normal weekly water change. Siphon out say 1/3 of the water. Then in a pail mix half tap, half distilled. Conditioner it, and pour it in. Several pails will be needed obviously. But the change will be gradual. I would be inclined to do this twice weekly. Test the tank hardness and Ph a few hours following each change to monitor progress.

SinCrisis is correct, so monitor the pH along with the hardness. The latter may not change much at first, but don't do anything to force it.

I have near zero hardness in all my tanks (except the one with the basic water fish) and I let the pH drop where it will. But I also have almost totally wild caught fish. And plants. The tank does stabilize. A pH drop is only a problem when the fish can't handle it, or if fluctuating.

Byron.


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## KendraMc (Jul 20, 2011)

i would imagine that this is one case where smaller, more frequent water changes would be a good idea, as it would cause the parameters to change more slowly.


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## Ami (May 27, 2011)

Just wanted a clarification before I actually start this eve.
My aquarium hardness is between 75 and 150 ppm. The tap water here is 300 ppm. So to get final hardness of 75 ppm is it better to dilute each gallon of tapwater with 3 gallons of distilled water? Or is it better to stick to the 50:50 ratio like Byron suggested?


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## KendraMc (Jul 20, 2011)

the 50:50 ratio would just halve your tap water's hardness. if you need a quarter the hardness, you would need 2 gal distilled to each gal tap water (i think, if my math is wrong, please correct me)


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## Byron (Mar 7, 2009)

True, but the thinking was a more gradual change. This may be overly cautious, but...

My previous thinking was to do half/half with each pail of water at a water change. If you change 1/3 of the tank, and replace that third with water that is half the hardness of the tap, it will lower the total hardness in the aquarium by some amount that will not be stressful. You could even do more frequent water changes. another in 2 days, same thing. Then another in 2 days, etc. This is quite gradual over a period of 1-2 weeks. Each time, the replacement water istself is half/half.

Another approach would be to remove 1/4 of the tank and replace it solely with distilled water. That reduces the hardness by 1/4, which is probably not a problem. Wait a couple days, repeat. The subsequent changes will of course be slightly less each time with respect to the hardness, so more gradual as they go, as far as immediate changes.

I've never had to do this, having such soft tap water. And while many have written on pH changes being gradual, there is little on the hardness.

Byron.


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## KendraMc (Jul 20, 2011)

Byron brings up a good point. what is the pH of your tap water compared to the pH of the distilled. usually the pH is related to the hardness, so i'm going to guess you are trying to lower both. pH does not change as consistently as hardness, so smaller additions of distilled water might be helpful. test your pH regularly for a while, since by adding the distilled water you are limiting your water's buffering ability and pH can become unstable, which would be very bad for your fish.


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## Ami (May 27, 2011)

KendraMc said:


> Byron brings up a good point. what is the pH of your tap water compared to the pH of the distilled. usually the pH is related to the hardness, so i'm going to guess you are trying to lower both. pH does not change as consistently as hardness, so smaller additions of distilled water might be helpful. test your pH regularly for a while, since by adding the distilled water you are limiting your water's buffering ability and pH can become unstable, which would be very bad for your fish.


The tapwater pH is 8.3 and hardness is 300 ppm.

I'll keep an eye on the pH & hardness as you & Byron have suggested.

I think I'm going to add the following mix when I do water changes. The tap water is 300ppm and since I have two 5 gallon pails, I'll dilute 3.5 gallons distilled water with 1.5 gallons tap water (in each bucket). This should give a hardness of 90 ppm (eventually). Hopefully the pH will not swing too wildly. Once the hardness and pH seems stable, I see if I want to shoot for 75 ppm hardness.


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