# Questions about ro/Di units



## 916 (Mar 27, 2011)

I'm gonna be purchasing a ro/Di unit from bulk reef supply I have a couple of questions when the water runs thru the system and into say a clean trash can do I still have to add declorinator to the water and can I use the waste water to do water changes for my fresh water tanks and would I need to add declorinator to that


----------



## bmlbytes (Aug 1, 2009)

You do not need dechlorinator for RO/DI water. I would not use the waste water for other fish, it will be extremely hard. If you did, you would probably want to use the dechlorinator on it. Most people use the waste water for something else. For example, someone I once knew used the waste water for his washing machine.


----------



## 916 (Mar 27, 2011)

O I thought that the waste water was cleaner than the water that came in also for you guys with medium sized tanks 55-100 gallons did your water bill go up by a lot since it wastes so much water


----------



## Fishpunk (Apr 18, 2011)

No that's not the way RO works. RO is forcing water through a membrane and the dissolved solids get left behind. Twice as much waste water is created than RO water, and all the hardness that was in the RO third is now in the waste water. 
I wouldn't put it into the washing machine either, not good for the clothes. Better to water plants with it. I'm not convinced the chlorine is removed in the RO process. Personally, I use dechlorinater in what little RO water I use as it doesn't really harm anything.


----------



## bmlbytes (Aug 1, 2009)

Oh yeah, I forgot. The chlorine is removed by most RO/DI systems, but only because most have a carbon pre/post filter on them. It is necessary to prefilter the water with a micron filter so that the RO membrane does not get clogged, and almost every RO system uses a carbon filter for either 1 of 2 prefilters or as a post filter.


----------



## kay-bee (Dec 6, 2006)

bmlbytes said:


> ...The chlorine is removed by most RO/DI systems, but only because most have a carbon pre/post filter on them...


That's correct. The carbon block stage(s) will adsorb the chlorine. When filtering chloramine-treated tap water the carbon block breaks the chlorine-ammonia bond of the chloramine and adsorbs the chlorine. The freed ammonia passes through the carbon block stage and RO membrane where it is removed by the DI resin.


----------



## Fishpunk (Apr 18, 2011)

Assuming regular maintenance is done. A seven year old carbon filter is worthless.


----------



## kay-bee (Dec 6, 2006)

7 years?

Depending on how much water the hobbyists makes, the carbon block(s) should be changed out every 6-12 *months*.


----------



## Fishpunk (Apr 18, 2011)

kay-bee said:


> 7 years?
> 
> Depending on how much water the hobbyists makes, the carbon block(s) should be changed out every 6-12 *months*.


Exactly.


----------



## 916 (Mar 27, 2011)

Quick question I went to my lfs and they had 2 stage rodi units that were 25 gph they say that those waste less water is that true and do 2 stage rodi units work to clean the water


----------



## bmlbytes (Aug 1, 2009)

Some RO units are more efficient than others, so they will make less waste water. Are you sure its DI too? Two stage seems like its missing something.


----------

