# The Truth About Distilled/RO Water



## KARMAL (May 6, 2010)

I use a mixture of RO water in my tank in order to keep my pH down. I have heard that "pure water" such as distilled or RO water does contain the right properties in order to support aquatic life (including beneficial bacteria).

Is this true? Are there other aquarists here that mix RO or distilled water during water changes?


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## Rick_Lindsey (Aug 26, 2002)

hrm, you definately don't want 100% "pure" distilled/RO water. There are certainly fish that appreciate softer water than you will find out of most taps, and cutting your tapwater with RO is one way to lower the softness. There is a danger, however, of having a kH too low in the aquarium, since degrading organic matter can cause the pH to crash if the water has no buffering capacity. I suspect this is less of an issue in a soft-water lake or stream, since there is a vast quantity of water, however in your aquarium... not so much.

What sort of fish do you keep? What are your tap waters? RO is the last thing you want if you keep african rift lake or even some central american cichlids. It may be a viable way to reduce the hardness and alkalinity of your tapwater if you're keeping south american or west african riverine cichlids.

-Rick (the armchair aquarist)


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## Rick_Lindsey (Aug 26, 2002)

Distilled/RO water is often used in salt water since it's a "known", to which they can add measured amounts of salts to bring the water to be exactly what they want, and you could do that for freshwater aquaria too, but it's a little overkill in most cases.

-Rick (the armchair aquarist)


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## KARMAL (May 6, 2010)

Rick-

My tank set-up is in my signature. 4 Bolivian Rams and friends. My tap water is quite hard, around 7.8-8.0. I use a little less than 10% RO water total to get a more neutral balance of 7.4-7.6.


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## kmuda (Nov 27, 2009)

As long as you are mixing distilled/ro water with harder water, no worries. You are fine.

Distilled water is totally void of trace elements, salts, and necessary buffers. Your tap water is full of the stuff. Especially at only a 10% mix, the water you are placing into your tank will contain the necessary elements.


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## Number6 (Mar 13, 2003)

I have kept many soft water fish in "pure" R/O water... although it is devoid of anything to stop pH swings (can be harmful in conjunction with other things) and it is devoid of any life supporting elements, it is not lethal for all life forms (contrary to popular suggestions).

I prefer to think of it as simply pure H2O... so if I take 50% R/O water with a KH of 0 and tap water with a KH of 10, I end up with water with a KH of 5... If nothing else, it cures anyone ever thinking of R/O water as some sort of poison that they need to counteract! :lol:


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## redblufffishguy (Jul 16, 2009)

There is a product out there called "R/O right" they claim using this product, you can use 100% RO water. I have not tried it, but have a buddy who did for years. Even bred discus with it.

It's worth looking into if controlling your PH is that hard!

RBFG


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