RO vs DI water - the difference ?

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westwind77

Member
So what can RO water provide me with DI water can not? I have an API 'tap water filter' that I use, from what I can tell the water is great that comes out of it. I have 0 phosphates, nitrates, nitrites when I test it before it goes into the tank. What does RO remove that DI does not?
I still have a minor algae issue so I am wondering if I am missing something and need to switch to RO and use the DI at the end like I see some systems offering.
Thanks!
 
uneverno

uneverno

Active Member
It's actually the reverse. DI removes mineral salts, in particular for our purposes, silicates (which feed algae), that RO alone does not.
In a typical RODI system, the water is put through the RO portion first to remove most of the impurities, and then the DI to remove anything the RO can't get.
RODI water is purer than distilled water because the DI unit removes dissolved gases (such as CO2) which are still present in distilled water.
 
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westwind77

Member
So, what "impurities" does an RO system remove that a DI only system does not? If a DI filter does such a good job why run a RO system?
Does an RO system reduce dissolved solids? If so, how do they negativly affect a system?
 
scsinet

scsinet

Active Member
Solid particulate matter is not removed by the DI process.
However, by and large, water that is filtered by DI alone is more suitable for use in an aquarium than RO alone.
But it all comes down to cost. DI resin is very expensive and lasts a VERY short period of time when removing the same amount of impurities as an RO membrane.
As a hypothetical example... X pounds of DI resin may treat 1000g of water that has been pre-processed by RO. But that same amount of DI resin may only last for 15-20 gallons if used alone.
RO membranes last for tens of thousands of gallons and do most of the "heavy lifting." The DI resin just has to come in and finish the job.
Plus, with RODI all solid particulate matter is removed.
 
W

westwind77

Member
Originally Posted by SCSInet
http:///forum/post/3023460
Solid particulate matter is not removed by the DI process.
However, by and large, water that is filtered by DI alone is more suitable for use in an aquarium than RO alone.
But it all comes down to cost. DI resin is very expensive and lasts a VERY short period of time when removing the same amount of impurities as an RO membrane.
As a hypothetical example... X pounds of DI resin may treat 1000g of water that has been pre-processed by RO. But that same amount of DI resin may only last for 15-20 gallons if used alone.
RO membranes last for tens of thousands of gallons and do most of the "heavy lifting." The DI resin just has to come in and finish the job.
Plus, with RODI all solid particulate matter is removed.
Exactly what I wanted to know! Thank you!
 
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