I currently have a 10 gallon (38 L) tank with the following fish:

  • 1 male dwarf gourami;
  • 6 glowlight tetras (4 female and 2 male).

Here's my current setup:

  • "Aqueon 10" filter (labeled as being appropriate for 10 and 20 gallon tanks);
  • 1/4 inch (0.63 cm) of gravel;
  • a medium-sized rock (4-5 inches / 10-13 cm thick and high);
  • a small piece of driftwood (8 inches / 20 cm long, a few inches / some centimeters thick);
  • 5 small fake plants of varying heights.

So, I'd like to move the fish, along with all the water, gravel, rock, driftwood, plants and the filter into an empty and clean 20 gallon / 76 liters tank (it's a "20-high"). Because the intake tube extends 8 inches into the tank, I figure that it would probably only take an additional bucket of water (1.5 gallons / 5.7 liters) to bring the water level high enough for the filter to work correctly. Then I will add more water over the next few days/weeks until the tank is at full 20-gallon (76 liters) capacity.

I'm hoping that keeping the same water, filter, and substrate will make the transition easy and as gentle as possible on the fish.

Does this sound like a good plan?

BTW, I've been doing 20% water changes on a weekly basis and I replace the filter cartridge every 2-3 weeks.

2 Answers 2


Yes, this will be perfectly fine. Reusing the filter and substrate means you're effectively transferring the biofilter, so this is a very different scenario than moving them to a brand new setup. In fact, all you're doing here is replacing a single piece of equipment on the existing system; it just happens to be the piece that holds all the water.

I'm assuming, by the way, that the tank is in the same house. If they're going from one location to another, there are more things to consider that I'll leave aside for now.

Moves are always stressful on fish, but you can minimize a lot of that if you have someplace to hold them while you're breaking down the old tank and setting up the new one. I'd recommend stopping by the hardware store and picking up a cheap 5-gallon bucket: you can fill it with about 3 or 4 gallons of tank water, put an airstone in and cover it loosely (to prevent jumpers), and then your fish can hang out there while you work.

When you move the substrate, you're probably going to kick up a shocking amount of crud if the tank has been running for any length of time. You don't want to move this grossness over -- it's just rotting food, feces, etc. I'd vacuum it before taking it out or rinse it (with tank water) in a strainer.

The other thing to note about the gravel is that you're going from a tank with 1/4" gravel over a 20" x 10" footprint, which comes out to 50 cubic inches. The new tank has a 24" x 12" footprint, so the 50 cubic inches will only cover the bottom to about 0.17" deep. So you may want to add some more.

Once you move the new fish in, there's no need to bring it up to the full 20 gallons so slowly. You may want to take a few hours to fill it completely, but except for the stress of the move, this is not much different than doing a big water change in the 10 gallon. The important thing with acclimating fish to new water is not the volume per se but how quickly the water parameters change; if the new water matches the old water closely (which it should here, since it has the same source), acclimation is less of a concern. If you want to be cautious, you could add about 20% of the volume each hour, but I don't think you'll gain much by going slower than that.

Other than that, the move should be pretty straightforward. Watch the fish carefully for the next few weeks after the move, since the stress will weaken their immune system a bit. And monitor the ammonia and nitrite levels daily for the first week, just in case the move disrupts the biofilter (which would be surprising, unless it dries out). But once everything is settled in, the 20 will be a better environment for them than the 10.

  • 1
    Good points. I'd recommend that you get a "food safe" bucket though (perhaps something designed for washing up?) as there are different types of plastic and not all are safe for food - I think it's probably safest to put the fish in one that is. Commented Jul 23, 2014 at 14:01
  • I disagree about the new and old water matching though. Just because they originally came out of the same tap doesn't make the fresh water similar at all to the water that the fish have been living in for months. Commented Jul 23, 2014 at 14:15
  • Good point about moving the fish to a separate container during the move operation. I hadn't thought of that. Commented Jul 23, 2014 at 15:35
  • @starsplusplus I think the water will be okay. He's been doing 20% water changes weekly, so it should be reasonably close to tap. If he can keep most of the original water, it's the equivalent of a 50-75% water change. Slow acclimation over a few hours should be okay for the fish, easier than coming home from the fish store.
    – toxotes
    Commented Jul 23, 2014 at 15:42
  • Re: the bucket, totally agree materials are a concern with repurposed fish supplies. I think the main short-term risks with plastics specifically comes from higher temps than we'll see in normal aquarium uses, though you have to watch out for hoses and things that are treated with pesticides or anti-algae stuff. In practice, I've used Home Depot buckets to hold animals/backup water for years, and my experience is they're safe for short-term use assuming they haven't been used for oils/other nastiness.
    – toxotes
    Commented Jul 23, 2014 at 15:46

Good on you for moving them to a new tank. That should give them more room. I did a similar move quite early in my fishkeeping days, and the following is a combination of what I did and things I would do differently now I have more knowledge.

You have exactly the right idea in keeping the water and components the same. That should minimise the impact of the change. Keeping the same water should minimise the stress to the fish and keeping the same filter should keep the bacterial consistency of the filter medium the same.

The biggest problem I see with your plan is the substrate: there's usually a lot of decomposing matter on the tank floor, and it might introduce more problems than it would solve to try to migrate the gravel without the decomposing matter. As soon as you start to try and shovel it up, all that decomposing matter will start floating around in the water. If it were me, I'd probably use the opportunity to buy new gravel. Rinse it thoroughly before adding it to the new tank to remove dust, soak it for 24 hours in dechlorinated water (or tank water if you have any to spare), discard the soaking water and then add the gravel to the new tank. In the old tank, suck the water up until about an inch off the floor (point the tube at the edge rather than the bottom of the tank, to avoid sucking up the decomposing matter) to go into the new tank, then ditch the last inch's worth of water and the old gravel.

Alternatively, to keep the gravel, I'd say suck the water up as above, leaving the gravel undisturbed for as long as possible, then take the gravel out, put it in the sink and rinse it thoroughly to get rid of all the debris and dirt. Ideally you'd rinse it with tank water, but it'll probably need quite a bit of a rinse, and the water you use to rinse won't be useable for the new tank since it will be full of decomposing matter. On balance I think it's better to rinse with tap water and have more water to put in the new tank. Then add it to the new tank and continue from there. This might be a better option than replacing the gravel entirely, since you'll lose the decomposing matter but still have any algae etc. that are on the old gravel, and don't risk altering the pH or introducing new solutes into the water with the new gravel.

You've got the right idea with the water changes as well. Too much of a change will stress the fish, and fresh water from the tap is completely different from water they've been living in for a while. Starting off with the minimum you need to allow the filter to work is a good idea - they're going to be stressed enough from the move anyway without a huge water change. I'd leave it at least a week before adding more, but also test the nitrate/nitrite and pH before and after moving, to see if anything's changed.

As long as the tests are okay, I'd consider adding 20% more at a time, as if it's just a normal water change. So after the move you'll have 11.5 gallons. You could add 2.3 gallons in the first water addition, then 2.8, then 3.4, which would take you up to 20 gallons. If you want to stay on the safe side, you could reduce those a bit so it would take you one more change to get up to 20.

Of course, if you get an ammonia or nitrite spike, you'll probably want to change some water as well as adding some. So you could take out 10% and put in 20%. You'll get to 20 gallons more slowly that way but it will enable you to remove some water as well as just adding.

Finally, I'd recommend leaving the filter cartridge in there for a bit longer so as not to disrupt the filtration system (in terms of bacteria and so on) too much. Alternatively, or additionally, rinse it at your next "change" instead of discarding it entirely. When I kept fish I had a filter which had two spaces to put the medium, which allowed me to change only half at a time, which was great for keeping the bacteria consistent. I'm not sure from your description that you have one like that but rinsing it would have a less dramatic effect than binning it and starting afresh.

  • Good points about the gravel gunk. I don't like the bright blue color of my current gravel so I'll probably just put new substrate down in the 20 gallon. Thanks! Commented Jul 23, 2014 at 15:35
  • It turned out that I had to fill the tank almost completely full to get my filter to start up again. The Gourami has been sluggish lately, water tests don't reveal the presence of any nitrites, and very little nitrate. Been keeping an eye on things and I think he'll pull through. The tetras seem much more active, which has been fun to see. The new gravel looks nicer too. Thanks for the advice! Commented Aug 9, 2014 at 5:43

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