# RO water need to be dechlorinated?



## jackmerius27 (Oct 23, 2015)

I just put some RO water in my tank, no dechlor, then a bunch of fish died. Any connection? Did I make a rookie mistake?


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## lksdrinker (Feb 12, 2014)

I'd bet your mistake lies in the fact that you changed your tank parameters by introducing this "new" water not in neglecting to use the dechlor. Your new RO water Likely has a different PH than what you get out of the tap and both are likely different than what was in your tank. RO water should not need dechlor. while the r/o process does not remove chlorine the carbon portion of the filter should handle the chlorine without issue.


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## shrimpNewbie (May 6, 2011)

lksdrinker said:


> I'd bet your mistake lies in the fact that you changed your tank parameters by introducing this "new" water not in neglecting to use the dechlor. Your new RO water Likely has a different PH than what you get out of the tap and both are likely different than what was in your tank. RO water should not need dechlor. while the r/o process does not remove chlorine the carbon portion of the filter should handle the chlorine without issue.


This^ +1

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## Argus (May 22, 2013)

lksdrinker said:


> I'd bet your mistake lies in the fact that you changed your tank parameters by introducing this "new" water not in neglecting to use the dechlor. Your new RO water Likely has a different PH than what you get out of the tap and both are likely different than what was in your tank. RO water should not need dechlor. while the r/o process does not remove chlorine the carbon portion of the filter should handle the chlorine without issue.


I suspect it was the radical change in GH, KH, and TDS that killed the fish, rather than pH. There is some evidence that "pH shock" is really TDS shock. 

I use RO water for my water changes without dechlorinization. However, I remineralize the RO water with 



 and 



. Equilibrium increases GH and potassium bicarbonate increases KH. 

When doing major water changes (more than 25%) the new water should be fairly close to the aquarium water in GH, KH, and TDS.


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## flight50 (Apr 17, 2012)

I would get a water report from you city. Most large cities have gone to using chloramines instead of chlorine in the municipal water supply. A regular RO using does not remove chloramines. They are much harder to break down vs chlorine as it prevents more bacteria growth in city pipes which is why they use it. Therefore adding a chloramine filter is best. A chloramine filter uses catalylic carbon for this. This is considered a 4 stage RO system. Mine is a 3 stage that includes the DI portion and I added the separate filter for chloramines. When I was low tech on my 29g, I use to do 75% water changes bi-weekly using straight RO mixed with tap only before I started dry dosing fertilizers. I never lost a fish as they greatly appreciated the fresh water.


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## lksdrinker (Feb 12, 2014)

Argus said:


> I suspect it was the radical change in GH, KH, and TDS that killed the fish, rather than pH. There is some evidence that "pH shock" is really TDS shock.
> 
> I use RO water for my water changes without dechlorinization. However, I remineralize the RO water with Seachem Equilibrium and potassium bicarbonate. Equilibrium increases GH and potassium bicarbonate increases KH.
> 
> When doing major water changes (more than 25%) the new water should be fairly close to the aquarium water in GH, KH, and TDS.


Very true! I mentioned water parameters but only specified ph. Mentally I intended to include all testable parameters!


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