I get RO, but why DI?

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caymanada
Amoeba
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Joined: Sat Jul 08, 2006 9:02 pm
Location: West Mobile

I get RO, but why DI?

Post by caymanada »

I understand why RO water is great, because it removes sediment, chlorine, flouride, phosphates, organics, etc...I get that.

Why is deionized water so important for saltwater aquariums?

The deionization process removes mineral ions such as sodium, chloride, calcium, magnesium, potassium, etc. All of which are found naturally in sea water and are added back to the water before being mixed in the tank. So why go to the effort, and expense, to remove them?
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Amphiprion
Astrea snail
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Re: I get RO, but why DI?

Post by Amphiprion »

There are certain things that membranes are rather less suited for as far as removal is concerned. The same is true of DI resins. Both complement each other quite well. In typical cases, membranes are good at removing larger molecules and particles that are tightly bound with water molecules. DI resins, on the other hand, are well suited to very small charged particles, like many of the common ions out there that would normally pass through membranes. The RO membrane itself is pretty good at getting rid of most things, at least to a degree. DI resins scrub what is left to near zero concentrations. Phosphate and silicate are some ions that aren't removed as readily by most membranes (though some very expensive ones can remove higher quantities). It is cheaper, however, to employ resins, which, when cared for, last a good while to get rid of the remainder. Some people, such as myself, use multiple DI canisters after the membrane to make sure water is as pure as possible, ruling out anything else sneaking by. It is also a buffer in case the membrane dramatically loses rejection rates.

Another potential reason is that DI has a 0% waste rate, whereas most membranes waste nearly 4x as much as they produce. The combination also helps in this regard, since you don't waste any more water than you have to.
Andrew

25g planted nature aquarium
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