RO, DI, DW Differences?

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lucky777ca

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Jan 25, 2006
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RO water is water that is passed through a semi-permeable membrane and extracts the larger solutes found in the water (at least that's what I think it is). This would make the water softer (in the sense that the larger organic molecules are trapped by the membrane, while other smaller molecules are passed through).

DI (de-ionized) water is water that has been stripped of cations (positive ions, such as K+, Na+, Ca2+, etc.) and anions (such as Cl-, Br-, etc.), with the exception of the hydronium ion (H3O+) and the hydroxide ions (OH-), which is always present in minute amounts due to the autoprotolysis of water. This method would make softer water (in the sense that there are any Ca2+ and Mg2+ ions present), but still contains organic molecules water, which are neutral and non-ionic.

Distilled water (DW) is water that has been steamed repeatedly in order to removed solutes found in the water. With every heating & cooling of the water, the concentration of the solutes in the water decreases, therefore, slowly creeping towards a highly pure water (pure H2O, although not completely, as there might still be minute amounts of solutes present).

Anyways, would there be any significant differences between the three? Could they be used interchangeably in using as water for a tank? For example for breeding tetras.
 
NO!

DW, as I am familar with, contains contaminants with are released with the steam.

TR


BTW:

I do not understand the nature of your question.

A still could be fabricated for a burner on your stove but the capatilized annual cost, and this is just an educated guess, would be much greater than a 60GPD RO/DI unit.
 
I wasn't thinking about making distilled water. :) That would be too costly, as you said. I was thinking about those that are sold at the stores.

As for the nature of my question, just wanted to know if you would be able to use distilled water from the store, instead of RO water from the store (according to my brother, I think that RO water is being sold)... or DI over RO. That's pretty much it :D
 
Sure, as far as tetras are concerned it's all the same stuff, water with very low TDS.


You'd be hard pressed to find DI water that hasn't been run through first charcoal (to get rid of chlorine, mostly, but also various organic impurities), then through a RO membrane (to get most of the other disolved things out). Otherwise the DI resin has an incredibly short lifespan.


If you're planning on continuing to use nearly-pure water i recommend spending the $120 on a RO+DI unit off ebay. Thats between 120 and 500 gallons of water depending on how you buy yours, but it's right in your home so you don't have to buy gas or lug bottles into the store. Even if you only have a single 40g tank that you do 50% changes on each week the RO+DI will pay for itself in half a year, and that isn't counting gas money.

Plus it tastes good.
 
Distilled water is not a good option and I would rather go with RO water over it. DW has absolutely nothing in it, unlike RO water which rarely spits out pure h2o.

I tried DW for a few months and realized that I was so far lucky but was walking on thin ice. Using DW water can lead to serious water chemistry swings if anything is added. If you want to not use tap (which shouldnt be a problem unless levels are extreme) than go with a RO/DI unit like bobnova suggested.

Using store bought water isnt the most effective way to do water changes, especially if you run into an emergency...
 
Thats a point i forgot. Using genuinely pure water* in fresh water tanks leads to roughly the same thing that happens when you eat ramen and nothing else for months on end.
Mineral deficiencies!

From that standpoint, unless you're doing a marine tank where you're mixing "salt" in to make the proper formula of water, you're better off just using RO water without the DI.
The 5% of tap water TDS it leaves behind contains some beneficial minerals that you don't really want to be without.
(One of the things that DW water lacks is KH, with 0kh the cycle bacteria cannot function or live. Sometimes if you have a substrate that has the proper minerals in it the DW water will slowly dissolve it and give you a KH reading)




*Not really genuinely pure, genuinely pure water etches glass and dissolves pretty much anything. You won't find it outside a chemistry lab.
 
Bobnova said:
Thats a point i forgot. Using genuinely pure water* in fresh water tanks leads to roughly the same thing that happens when you eat ramen and nothing else for months on end.
Mineral deficiencies!

From that standpoint, unless you're doing a marine tank where you're mixing "salt" in to make the proper formula of water, you're better off just using RO water without the DI.
The 5% of tap water TDS it leaves behind contains some beneficial minerals that you don't really want to be without.
(One of the things that DW water lacks is KH, with 0kh the cycle bacteria cannot function or live. Sometimes if you have a substrate that has the proper minerals in it the DW water will slowly dissolve it and give you a KH reading)




*Not really genuinely pure, genuinely pure water etches glass and dissolves pretty much anything. You won't find it outside a chemistry lab.
Click to expand...

:iagree:

That was another thing that people told me when I asked about DW. Fish need certain trace minerals to survive and function properly. DW lacks most minerals.

If you dont mind me asking, why not use tap water???
 
Would tetras still breeding in a pH of 6.0 or so, without changing the hardness of water (which is pretty much my reason of getting water which is softer)? If breeding is just the reason, so tap water that's peat filtered should be sufficient in order to trigger them to breed?

Anyways, I guess the DW that I get should just be used for my VFT (Venus Flytrap) in my 5.5G aquarium :D
 
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