What is the magic of RO/DI Water?

Jan Cavalieri

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I just ordered a RO/DI system - it's portable - hooks on to a kitchen sink and makes about 75 gallons of clean water a day. I've ordered several Rubbermaid trashcans (the only kind on the market that is "food safe" and doesn't leech chemicals in the water. These will each have dollys so I can roll the water down the hall to my "fish room" since there is no way that I know of to move that much water.

I have several freshwater tanks that I've always used tap water that included (in each bucket) Prime and a Neutralizer chemical to change my PH 9.4 water to exactly PH 7. (it does drift down to about 6,5 during the week but a waterchange pops it back up to 7 and I do weekly waterchanges of 60-70%). I've been told that my PH is so bad, that I should use a RO/DI water system and use that water but the more I read up on what that system does to water the more hesitant I am.

Now I'm moving into saltwater/reefer tanks which require RO/DI water. They also require a PH of 8 or so. I assume that when I add the salt it will include the trace elements that saltwater life needs to stay alive and will adjust the PH accordingly?

So my question is - what is the PH of RO/DI water if I used it for my freshwater tanks. Unlike my saltwater tank, It would be devoid of any trace elements needed by freshwater fish, unless there is some chemical mix of stuff that you can buy to add them back to the RO/DI freshwater tank?

I've also read that by itself, RO/DI water really has no PH because it has no substances to provide a buffer. So I am curious - can I even use this water in my freshwater tanks? Or will I be restricted to using it only for my saltwater tank?
 

Essjay

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Pure water has a pH of 7.0 at 25 deg C.

But most RO water is not 100% pure, most still has a tiny amount of dissolved things which can affect the pH.

For fresh water, it is usual to either mix it with tap water where that is hard to put some minerals into the mixture, or to use remineralisation salts to get the GH at the desired level.
 

hansgruber7

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I use RO/DI water on my freshwater tanks. You need to remineralize it. I use Seachem Equilibrium and I stabilize the PH with Seachem Aqualine and Acid buffers. Has been working well for me for quite some time. My tap water is unusable.
 

PheonixKingZ

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Pure water has a pH of 7.0 at 25 deg C.

But most RO water is not 100% pure, most still has a tiny amount of dissolved things which can affect the pH.

For fresh water, it is usual to either mix it with tap water where that is hard to put some minerals into the mixture, or to use remineralisation salts to get the GH at the desired level.
So you will have a low water hardness if you use RO/DI water?

That could be an issue for me, once I get my system. (My saltwater tank needs to have a much higher pH than freshwater tanks)
 

madmark285

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So you will have a low water hardness if you use RO/DI water?

That could be an issue for me, once I get my system. (My saltwater tank needs to have a much higher pH than freshwater tanks)
Yes, RO will remove the majority of the minerals in the water. I don't know this answer but do you really need RO unit for a fish only saltwater tank?
 

Essjay

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This is what Pheonix was told in another thread
I have to use fuplie RO water? Why?

Ro water makes sure there are no contaminates that will harm corals and helps keep your water stable. Also using tap water will make you tank an algae tank.

Regarding R/O water, if your tap water is clean and free of nitrates, then you can use that. However, if your tap water is like the stuff in the UK with high nitrates and all sorts of other stuff, then you should use R/O water for making up the sea water.

R/O water is more important if you keep corals, and less of an issue with fish only tanks.
 

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So my question is - what is the PH of RO/DI water if I used it for my freshwater tanks. Unlike my saltwater tank, It would be devoid of any trace elements needed by freshwater fish, unless there is some chemical mix of stuff that you can buy to add them back to the RO/DI freshwater tank?

I've also read that by itself, RO/DI water really has no PH because it has no substances to provide a buffer. So I am curious - can I even use this water in my freshwater tanks? Or will I be restricted to using it only for my saltwater tank?

This needs explaining to avoid misinformation. And I am only responding with respect to your freshwater fish tanks questions, not marine.

Each species of freshwater fish has evolved to function in very specific water parameters; there are some species that have a wider tolerance than others, but for the sake of this discussion let's take the majority. Many, in fact just about all species that live in very soft water such as the Amazon basin, do not need any mineral in the water; they don't have it in nature, they don't need it in the aquarium. Ian Fuller [an authority on Corydoras species] keeps his wild caught Corydoras in pure RO. My tanks are all zero GH/KH because (luckily for me, as I like the soft water fish) that is what comes out of my tap--our water here is zero GH/KH. These fish thrive in this, because they are designed to by nature.

Other species that live in water that has calcium and magnesium (the basic GH minerals) need those, and if the tap water source is not sufficient, they must be added. Livebearers for example would die in my water without mineralization to increase the GH (and pH, this tends to follow when we are dealing with RO). There are other fish in between, needing some re--mineralization. But it all depends upon the fish species' natural requirements, and our being able to provide them. Not all fish can live well in the same water parameters.

The pH of pure RO water would be 7, neutral--neither acidic nor basic. Such water does not exist in the habitats of fish because water is a powerful solvent, and readily assimilates substances it comes into contact with, such as minerals dissolved from rock or organics causing acidic water. Rain begins as pure condensed water but as it falls it usually assimilates CO2 making it acidic; depending where it lands, it may assimilate other substances, changing its composition respecting GH, KH and pH.
 
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Jan Cavalieri

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The majority of fish in my tanks are in the "moderately hard water" group. They all require a PH between 6.5 and 7,5. Once I adjust my PH to 7 (rather than the PH 9.4 in our city water) all seems pretty good, except I seem to have problems keeping some species for more than 6 months (haven't figured that one out yet) while others are 2-3 yrs old. The ones that live 6 months to a year tend to be my Gourami - my favorite fish, and while I've had some since I first established my tanks - I've lost others after about 6 months to a year. I'm not going to purchase any more of them until I figure out what is wrong. Their water requirements fit the parameters of my tap water with the exception of PH. I was thinking that since I was going to need RO/DI water for my future coral tank I have been thinking about using it for my freshwater fish as well - since it produces a PH of 7 that works for all my fish. But if the lack of trace elements are probably necessary it seems like RO/DI water is not the way too go.
 

Byron

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The majority of fish in my tanks are in the "moderately hard water" group. They all require a PH between 6.5 and 7,5. Once I adjust my PH to 7 (rather than the PH 9.4 in our city water) all seems pretty good, except I seem to have problems keeping some species for more than 6 months (haven't figured that one out yet) while others are 2-3 yrs old. The ones that live 6 months to a year tend to be my Gourami - my favorite fish, and while I've had some since I first established my tanks - I've lost others after about 6 months to a year. I'm not going to purchase any more of them until I figure out what is wrong. Their water requirements fit the parameters of my tap water with the exception of PH. I was thinking that since I was going to need RO/DI water for my future coral tank I have been thinking about using it for my freshwater fish as well - since it produces a PH of 7 that works for all my fish. But if the lack of trace elements are probably necessary it seems like RO/DI water is not the way too go.

My only comment here is, that the GH is far more important than pH as the mineral (or lack thereof) in the water affects the physiological functioning of freshwater fish. RO is zero GH, so this is not going to work, you will need to add minerals back into the water.
 

hansgruber7

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My understanding is that you also have to consider your shrimp and snails. They need a certain GH and KH to thrive, that shouldn't be zero. That's why I have to remineralize my RO water because I have shrimp and snails in all my tanks.
 

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Reverse Osmosis (R/O) water is meant to be pretty close to pure water with a pH of 7.0, and a GH & KH of 0ppm. R/O water is also meant to be free of chemicals and heavy metals. This is accomplished by forcing the water through various membranes and filter media. However, there are different quality R/O units and some are better than others.

R/O units also waste a lot of water and the best units will have a 1-1 ratio, where they create 1 litre of pure water and have 1 litre of waste water. Other units will use more water to create that 1 litre of pure water.

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Depending on what species of fish you keep, will determine what you need to do with the R/O water to make it suitable for them.

If you keep soft water fishes like neon tetras, angelfish, Bettas, gouramis and Corydoras, they can live in pure R/O water or a mixture of your tap water and R/O water.

If you keep rainbowfish, common live bearers or Rift Lake cichlids, then you can add a Rift Lake water conditioner to increase the pH, GH & KH or the R/O water. You can also use Rift Lake water conditioner to raise the pH, GH & KH of R/O water used for Cories, Bettas, gouramis, tetras, etc, just use it at a lower dose rate.

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Marine tanks can have natural sea water or artificial marine salts mixed with fresh water. Artificial marine salts have all the salt and minerals needed and worked out for you. So all you do is add some salt to some fresh water, and the minerals and salt will dissolve and raise the pH, GH, KH and salinity (salt level) to the level required for marine fish and corals.

Sea water should have a pH around 8.5 and a salinity around 1.022-1.025.
 
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Jan Cavalieri

Jan Cavalieri

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Well after considering all your replies I don't think I will use RO/DI water for my freshwater fish. I don't see that it would help that much and for environmental reasons it just has too much wastewater. My little bity reef aquarium is only 32 gallons, while my fresh water tanks will shortly be 6 gallons, 50 gallons and 100 gallons - that's a lot of water to waste when I think I'm doing an OK job managing the water myself. Mine is moderately hard or moderaletly soft depending on how you look at it but still within the range of softness required for Gourami. My water is spot on for Rainbow fish - I also have 6 bristlenose lemon colored plecos and 6 Dojo loaches - oh and 12 Chili Rasboras that were meant to be company for my Betta but the Betta died the day I introduced them to his tank (I did a quick water change - which always stresses him out terribly and then added more stress by adding 12 baby fish to his territory.) I should have known better than to stress him that much. These Chili's were basically fry when I got them and I luckily had some fry food - but they wouldn't eat it, so I ground up my regular flakes into tiny pieces and they don't seem to care much for that either. As far as I can tell I only have 4 left which ticks me off since I paid for 12. But I haven't found any carcasses - with my bad eyes I need a magnifying glass just to see them.
 

madmark285

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Each species of freshwater fish has evolved to function in very specific water parameters; there are some species that have a wider tolerance than others, but for the sake of this discussion let's take the majority.
The ability to adapt is a primary force in evolution, species that require very specific environments tend to go extinct. One should not assume that a freshwater species requires the specific water condition of its native habitat, it may be able to adapt and thrive in other environments.

One example is Zebra Mussels which are thriving in the frigid waters of the Great Lakes and now are found in the warm inland lakes of Texas. Another example for aquarium fish is the Hillstream loach which many assume they require cold fast moving waters yet there are reports of breeding Hillstream loaches in aquariums with warm calm waters.

Corydoras may thrive in zero GH/KH water but they seem quite capable of adapting to other water conditions.
 
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Jan Cavalieri

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I've seen that to some extent in my own fishes. I actually had two Hillstream loaches- they were so cool - and while they put up with the warm tank water quite well they spent most of their time under the air bubbler. Kind of like a dog sticking it's head out of a window LOL. I do think a less than perfect environment often effects their lifespan. My two loaches died after some bizarre water change accident that took out most of the tank of fishes - my assistant and I never did figure out what we did and the water parameters were fine but as soon as we poured the first bucket of fresh water in they just nearly all starting dropping dead. We lost 17 fish that day and I think we had about 5 or6 left - surprisingly some of them were gourami, which I've always had problems with keeping alive for more than a year. That was a horrible day. She must have forgotten to add Prime or something - thats all I can think of. I'm the only one living in the house so I know those buckets are for water changes so I wouldn't use them for anything else.
 

Byron

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The ability to adapt is a primary force in evolution, species that require very specific environments tend to go extinct. One should not assume that a freshwater species requires the specific water condition of its native habitat, it may be able to adapt and thrive in other environments.

One example is Zebra Mussels which are thriving in the frigid waters of the Great Lakes and now are found in the warm inland lakes of Texas. Another example for aquarium fish is the Hillstream loach which many assume they require cold fast moving waters yet there are reports of breeding Hillstream loaches in aquariums with warm calm waters.

Corydoras may thrive in zero GH/KH water but they seem quite capable of adapting to other water conditions.

I was being very general solely to avoid complicating the issue further. The point is that her soft water fish do not need mineralization, as Colin_T also noted in his response. The adaptability issue is a complex one, and not useful to get into here.
 

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