Methods for dealing with Chlorine

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Registered Member
Jun 18, 2021
Hey All,

I'd like to discuss safe methods for dealing with Chlorine.

I believe the safest method is to use a dechlorinator on a reserve water tank and aerating the container for 24 hours. We can siphon old water and muck from the aquarium, then add the resulting treated water in any amount of change water for your aquarium. The downside of this method is the cost of the reserve water tank. The upside here is safety.

The next method is dosing dechlorinator for the full aquarium volume. Basically, we are overdosing the dechlorinator to speed up its action against the chlorine, since our fishes will be exposed to chlorine for 2 minutes. What happens here is we siphon old water and muck from the aquarium (for example 25%), then add dechlorinator for the full tank volume, then add the desired amount of change water. Other people dose the dechlorinator at double or triple the change water rather than the full aquarium volume, I really don't know if its more effective. The downside to this method is that our fishes are exposed to chlorine for 2 minutes at water change. The upside is not having to buy a reserve water tank.

At the moment, I am deciding whether or not I should invest in a reserve water tank. If dechlorinator neutralizes chlorine in 2 minutes, would the risk of exposure to our dear fishes be monumental or insignificant?


AC Members
Jun 7, 2019
You will probably get various different opinions on this. Before expressing mine, one should also consider that in many places, such as using municipal water supplies, there is not only chlorine to consider, but also chloramine. The former will indeed dissipate after a while, under aireation, the latter will not, and must be chemically treated. Some dechlorinators treat both ammonia and chloramine, some don't.
If using well water, then the need to dissipate CO2 may be necessary.

I use municipal water, with chloramine. I have chosen to use a WDS (water delivery system), because after 2 catastrophic accidents in the past, I do not trust cities to always have the same concentration of chemicals, and because I like to adjust the temperature first, by mixing hot and cold water. One can do the same on the spot as when one has the hose from the tab to the tank, but I don't like that method (too dependent on whether my wife wants to do laundry at the same time, somebody is taking a shower or others, which affect water temp coming out of the hose and into the tank). A couple of times, nasties have come in the water due to the city doing something wrong, or seasonal changes, which affect water quality. Having a short-term storage tank gives me a second chance of noticing things like that, or warnings like funny smells in the water and makes me feel much better about it. It implies no extra work. The 55gal drums (food grade) I was able to get for free, but they can also be found fairly cheap. A sound investment.
Below, my WDS in the basement, from which I pump water to the tanks by using a Phyton hose and curved ending. Waste water goes outside to feed our gardens. Good luck!



Global Moderator
Staff member
Jan 11, 2013
West Falls NY
Real Name
Sorry if I missed it, but have you had problems using water treatment products?

On my 75gal tank that contains one oscar and one severum, I drain ~80% of the water weekly, dose with Seachem Safe then refill direct from the tap. My water supply uses a relatively low dose of chlorine. Been doing this method with these fish in this tank for 8 years.

One of my planted 55s gets a 50% weekly the same way.


AC Members
Jun 28, 2006
SF Bay area, CA
When our water companies used chlorine only, we often just aged the water to allow it to offgass, maybe a week in jugs (aeration would have helped)...or used any cheap dechlorinator if we were in a hurry (sodium thiosulfate). I did switch to Seachem Prime since they may "flush" the system at any time without warning, sometimes seasonally...I slightly overdose the replaced amount of water but also less than the entire tank volume. I just ballpark it.

Now I have chloramines & use Prime all the time. I dose a +/- capful before refilling the tanks with tap water. My smallest tank is 55g right now & all have lots of plants too. Plants use the ammonia pretty fast but can't deal with the chlorine aspect (bad for fish). I could "maybe" just use sodium thiosulfate...but I feel much safer using Prime...I don't have guess at dosing or hope for the best...or age my water. My tanks are too big to think water storage is a good option...& I don't need any excuse to put off water changes...sometime I do 1 tank, sometimes all 4...that would be a LOT of water...
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Staff member
Dec 30, 2005
Real Name
Mr. Normal
Just a note, public systems often shock their systems with the opposite of what is normally if they regularly use chlorine, they shock with chloramine, and the reverse.