# Difference between Distilled Water and RO water?



## hedge_fund (Jan 1, 2006)

I understand the process behind distilled and RO but how does each one differ when used in a shrimp tank? For example, I buy Poland Spring distilled water at the supermarket for my water changes and the PH is around 6.4 before adding it to the tank. TDS comes up as 0. What is the PH of RO water, is it safe to assume that it's the same?

I'm thinking of setting up an RO system just to get the PH even lower...I'm hovering around 6.2 in my tank but that's due to the HUMIC and Akadama that I have in there. I don't mind spending 2 bucks on distilled water to do my water change each week but if I can get the PH lower with RO then I'm game. The PH that comes out of the tap is around 7.5 - 7.6.

Reason why I want the PH lower is that I am interested in picking up some shadow pandas or BKK...CRS are breeding like crazy so now I need a new challenge. 

Thanks.


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## acitydweller (Dec 28, 2011)

i know my buddies who deal with reef tanks usually start with distilled water from the supermarket until someone coughs up the dough for an RO unit, then all the guys go to his house to bottle it up lol...

Just have to add back the traces and adjust to the params you're after in both cases. its way cheaper to start off this way since it may take several months before spending enough money to justify the cost of an RO but then again, the trips to stop and shop may wear on you as well...


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## mistergreen (Dec 9, 2006)

Distilled water is supposed to be more pure than RO (no minerals, 0gH). Both should be around 7pH.


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## hedge_fund (Jan 1, 2006)

acitydweller said:


> i know my buddies who deal with reef tanks usually start with distilled water from the supermarket until someone coughs up the dough for an RO unit, then all the guys go to his house to bottle it up lol...
> 
> Just have to add back the traces and adjust to the params you're after in both cases. its way cheaper to start off this way since it may take several months before spending enough money to justify the cost of an RO but then again, the trips to stop and shop may wear on you as well...


It's not really about the money since I purchase two gallons a week totaling 2 bucks. My issue with RO is that I don't want another aquarium contraption sitting on my counter. The only way I would go RO is if it's more beneficial than distilled but it seems to be the same thing.



mistergreen said:


> Distilled water is supposed to be more pure than RO (no minerals, 0gH). Both should be around 7pH.


Thanks...exactly the answer I'm looking for. Mine definitely does not have a PH of 7 though...I tested two different brands too in order to make sure. Unless my API test kit is inaccurate. 

So it looks like I'll continue with the distilled water since it actually seems better than RO. 

Anybody else has any comments?


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## mistergreen (Dec 9, 2006)

If you let water sit around, it should absorb CO2 from the air. That'll lower the pH a little especially distilled & RO since they have no buffers (kH).


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## GeToChKn (Apr 15, 2011)

mistergreen said:


> Distilled water is supposed to be more pure than RO (no minerals, 0gH). Both should be around 7pH.


Should be around 7 but not always. RO water pH is closer to the pH of the source water going in. Liam's tap or RO water is around 5. HolyAngels tap is 8.6, RO is still around 8 for him. There is no exact number RO water should be as there are many factors that determine the pH that even a RO filter doesn't touch.


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## slowgrower (Feb 7, 2012)

The difference b/w distilled and RO water is the process by which they are purified. 

Distilled water is water that is boiled and then condensing the steam. The condensed steam is the purified water.

Reverse osmosis (RO) water is water that is pressure filtered across a selective membrane. This membrane serves to remove a number of larger ions and molecules and its pretty effective. This is the same process used in desalinization.

In theory, distilled is "purer" than RO, but RO is still quite pure, especially for use in an aquarium. It is possible to further "polish" RO water through deionization and I know a number of reef keepers that do just that.

As mistergreen pointed out, both should have a pH near 7, but if left in an open container will absorb carbon dioxide from the air causing the pH to decease due to the lack of buffers.

In the grand scheme, RO water is cheaper and easier to produce and is more appropriate for home production. If you plan on doing some home distillation, I suggest whiskey

I guess what I'm saying is, if you don't mind lugging water around, distilled is great. If you want to make it at home, you will be looking to RO. If you want to lower the pH, you have to introduce an acid. Like you said, "I'm hovering around 6.2 in my tank but that's due to the HUMIC and Akadama that I have in there."

And to GeToChKn, if HolyAngels RO water has a pH of 8, he might want to consider replacing his membrane. Check the GH and KH, they should be close to 0.


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