View Full Version : RO v. RO/DI and removing ammonia

07-22-2010, 04:45 AM
Sooo... I've got a friend that I have introduced to the hobby by selling him an unused 55 gallon aquarium of mine. In making the sale I told him that I would help him along the way with any questions he had. I assumed he would set up a cichlid tank with fake plants or just a typical fake plant tropical community tank. Well... him and I are very competitive and him seeing my tank with live plants he decided that he would like to do this as well. Long story short... he has gone 0-60 with the hobby and taken it way further than I had ever thought was possible for him. (Really awesome)

He ended up buying a bogus RO/DI unit off ebay (I think) that isn't even rated for aquarium use. He has had his tank running for about 8-9 months now and doing really well but he keeps having an ammonia problem and I know it's not because his tank hasn't cycled or he has over loaded on fish. Free ammonia is at 0, but his total ammonia was still showing up. We figured out that there was still ammonia in his water after it had gone through the RO/DI.

Shouldn't an RO/DI unit remove ammonia from the water?? This is happening because he bought a crap unit right? or will ammonia make it through any RO/DI.

Secondly, I'm thinking of getting him a good RO unit (no DI) for his birthday coming up and I was wondering with a fresh water planted tank, is not having the DI portion going to make much of a difference for him? I know there will be a higher TDS amount, but is there any other disadvantage to not having the DI portion on the unit??

07-22-2010, 07:11 PM
Sounds like your friend is set on a planted tank. As a good RO system removes almost all the minerals from the water (like iron), I wonít think it would be a good idea to use RO water in a planted tank.

We do sell some RO systems were I work. I donít know very much about them, but based on some customer comments, typical problems to look for can include: old filter media, partially clogged membranes, and incorrect filter media in the unit.

Iím no chemist by any stretch of the imagination, but a properly maintained RO system will remove any molecule larger than a water molecule. If a ammonia molecule is larger than a water molecule than its gone, if not, most of it will get through. As none of our vendor promotional information states their systems remove ammonia (its not on the LONG list of things taken out) I think it would be safe to assume not all RO systems remove ammonia.

Iím not too sure if I helped, but I hope I did

07-22-2010, 07:29 PM
The DI catridge should be able to remove ammonia but his might have been used up and can no longer remove it because its performance levels are down.

07-22-2010, 11:19 PM
Is the DI cartridge the only membrane that will remove ammonia?? Will ammonia be removed in just an RO unit?

07-23-2010, 12:47 AM
Let me explain the whole process of RO/DI in more detail then.

Now, I'm not sure what brand he has but for my unit; there is a carbon prefilter, then RO, and DI. The carbon I use for my prefilter is catalytic carbon which does a better job than just activated carbon. So through the first stage of the prefilter, only some of the ammonia will be removed from the chloramine tap. The RO membrane will take care of it partially but not all. It also depend on the TDS and pH of the tap water as well. Finally, it's the DI unit that remove any residual ammonia.

Now, depending on the concentration of chloramine, TDS, and pH of the tap; it'll be the determinant of how quickly your membrane deteriorate.

07-23-2010, 11:05 AM
Spyder, what makes a RO/DI unit quality or garbage is the media you use. Many of the cheap units can actually take the higher quality media. You may be able to simply replace the media in his existing unit rather than buying hm a whole new unit.

As for the ammonia problem, what is the pH in his tank? If it is low enough, you won't ever have any free ammonia showing up. If he is having ammonium showing up then it's really inconsequential, but you may want to check on how much your friend is feeding the tank.