I recently moved my established aquarium from one room to another in the house. I had to remove most of the water so that I could lift the aquarium (with help!).

Once in the new location, I returned the original water to the aquarium and left the aquarium settle down for over six hours. At that time, the fish seemed to be happy and not showing signs of stress.

I added some new fish (three neon tetras and two fancy-tail guppies) to the aquarium - see this Q&A. The new tetras died very quickly thereafter. I had followed all the advice that I learned from the pet store and which agreed with most accepted internet wisdom regarding acclimatizing new fish to an existing aquarium.

Should I have waited longer to allow the fish to calm down more following the move?

EDIT: Further information follows regarding my set-up. The aquarium capacity is 100L, and the original occupants were three guppies, one angel fish, two albino catfish and the three neon tetras. There were two plants. The aquarium was well-established prior to the move - i.e. it wasn't part-way through a cycle. I am not able to test water quality.

  • 1
    There's a lot of information missing for us to help you. How large is your tank? What other kinds of fish live there? Was it cycled prior to removing the water? What were the water parameters, especially ammonia? Is your tank planted? How many tetras did you add at once? My guess is that it was an ammonia spike; it also could have just been that you got some poor-quality fish. But I really doubt it was because your current community was stressed unless you have more aggressive types.
    – Ozala
    Commented Jan 13, 2014 at 22:42
  • When you moved the tank, where did you store the fish that were in there? The fish that died - were they new fish, or from the tank? Commented Jan 14, 2014 at 16:16
  • @GrandmasterB: The fish remained in the tank as I moved it. The fish that died were new fish.
    – Nicholas
    Commented Jan 15, 2014 at 23:37
  • When you added the new fish to the tank, did you let the fish get used to the temperature of the water? Commented Jan 21, 2021 at 11:02

4 Answers 4


Honestly, I think you did fine. I think it's just because tetras, especially neon tetras, are sensitive to changes in water parameters, and your water was too different than the store's for them to handle.

Something to keep in mind too,is that angelfish are in the cichlid family, so can be pretty aggressive at times. Generally I'll see them act out when there's food, but fish do have different personalities.

What I do when acclimating new fish is to float the bags that the fish is in for about 20-30 minutes in the new tank. Make sure the lights are off, because the bags will be floating, the light will heat up the bag, stressing out the fish and keeping the temperature from matching right. After the 20-30 minutes have passed, I just cut a hole in the bag, and let the fish swim out. I will turn the light back on not long after the fish is out of the bag, but you can leave it off for a few hours if you're worried about the fish still. You can also add a little aquarium salt the day before, or even the morning of, adding the new fish, to keep their stress level low. I don't suggest adding anything as you're adding the fish, just because it's best to keep the water as stable as you can while they acclimate.

I would also suggest testing your water chemistry. You can get an aquarium test kit, or even take a sample of your water to stores like Petco and Petsmart to have them test it for you.

  • Thanks for your answer, much appreciated. Regarding the angelfish, I haven't seen any aggressive behaviour from it yet, but I have noticed that following the move, it has kept itself toward the back corners of the aquarium, and not swimming throughout the water as was the case prior to the move. I wonder if this indicates that it is more stressed than normal.
    – Nicholas
    Commented Jan 15, 2014 at 23:43

I would wait at least a week or two after moving an established tank to add new fish, and ideally closer to a month. Moving the tank does a few things to disturb its normal equilibrium, so it's just safer to wait until things have settled back down.

It's really important to monitor your water quality after the move. For one, in a lot of cases you're doing a huge water change -- probably 75% or more with a larger tank. If the pH, temperature, or hardness of the new water is dramatically different, this not only directly affects your fish, but your biofilter as well.

You also kick up a lot of detritus from the substrate. All this rotting food, fish waste, bacteria, etc. can easily impact your water chemistry -- it's potentially a lot more than the biofilter can handle right away. And the mechanical filter will have to deal with an above-average amount of, shall we say, fine particulate organic matter.

Also bear in mind that the existing fish have just gone through a highly stressful event. Even if the water chemistry is 100% perfect after the move, they're going to be more prone to health problems for a little bit. The immune system of a healthy fish will normally prevent the latent diseases in an aquarium from actually causing any sickness, but this level of stress can interfere with that. You don't necessarily need to treat the fish as if they're in quarantine after a tank move, but it's good to just watch them carefully over the next few weeks just in case. And any new fish is a potential source of new diseases as well -- it's safer to wait until your fish have settled in, rather than adding this at a point where they're more susceptible than usual.

This is sort of unrelated to the new-fish part of your question, but be extremely careful when you move a tank to get as much water as possible out of it. Water is shockingly heavy (when full, your tank weighs more than a grown man), and though the silicone holding a tank together is extremely strong, the shifting weight of water as it sloshes around can put mechanical stresses on side seams that aren't meant to be load bearing. If it's at all possible, try to take all the water, substrate, and decorations out of a tank when moving it, to prevent damage.

  • Thanks for your answer, much appreciated. Just to emphasise one point, I removed the water from the aquarium prior to the move, retained the water, and then returned the water to the aquarium following the move. There was no new water added to the aquarium in my case. Your comments regarding kicking up detritus etc are well made.
    – Nicholas
    Commented Jan 15, 2014 at 23:40

Something to note about the nitrogen cycle in aquariums is that the bacteria doesn't live in the water column. The bacteria mostly live in the filter media. As long as filter media stays wet, the bacteria will survive short periods without any nitrogen source.

There should be no reason for the aquarium to cycle when you move it, just remove the fish, empty the water (gravel vac), break it down, move it, set it up, put in water and acclimate fish. If you don't lose the filter media, there will be no ammonia or nitrite spike when the fish get reintroduced.

You can also note that fresh water (dechlorinated of course) has never hurt an aquarium. No need to move the water.


How much water did you leave in the tank? If you replaced all of the water (and replaced or rinsed/let dry the filter), it would need to cycle for 6-7 weeks before you can add fish to allow the nitrogen cycle to happen. Some companies sell a solution that can kick-start this, but they shouldn't be used to attempt to skip the cycling, which I didn't realize at first. The water should also be dechlorinated. I don't know if this is the problem you had, but it seems likely.

Here is an article that may help: "Nitrogen Cycle In Aquariums – An Easy Guide For Beginners". I hope this helps you.

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