I currently have a 15gal tank fully cycled. The tank is stock on the heavy side of thing and I purchase a larger tank (75gal) for another project I will not be doing finally. So I will use the larger tank to transfer the livestock of the small one when I move in about 2 week. I read the question "Is it safe to move fish and all equipment to a new tank?", but since the tank difference is much bigger I can't simply do as he did. Up to this point all is good, but now the new tank won't be cycled. The filtration on the 15 is an aquaclear30 with a double sponge filter.

I would like to avoid moving the livestock twice in a small amount of time. If I move the old filtration with the livestock could I simply add every one in the 75 and wait before adding anything else? I know the tank will be under filtered but in theory this setup handled the same bioload in the 15 gal tank.

The livestock currently in the 15 gal tank is 9 neon tetra, 4 zebra danios, 2 endler male, and 15-30 red cherry shrimps (not sure exactly how much I have in there... small baby factory).

3 Answers 3


A couple of weeks later, I have decided to tell you how I did it. It's been over a month since the transfer.

The other two answers were good, but they simply didn't work in my case. Since the larger tank was over 5 times bigger, keeping old water wasn't really an option. You need movement in the water so it doesn't become stagnant, especially over a 2 week period. Also since I wasn't just moving the fish from one tank to the other, it was harder to fill up the 75gal with tank water. They were in 2 different apartments, which made keeping water impractical.

Don't get me wrong, if it's practical to dump old tank water in the larger tank to fill it up partially at least, go ahead and do it. But if you are in a situation like me, where it is not practical, filling with tap water is correct. Since most of the good bacteria live in the filter and on other solid objects (substrate, decoration, plants, etc.), by transferring the filter, I had transferred the most of the bacteria.

Here's how I did the move. I had 20-40 red cherry shrimp and ~10 neon tetra, 4 danios zebra and 2 endler. I first removed most of the decoration from the tank. This was mostly plants, a couple of rocks and some wood. Then I started to drain the tank. I took the filter media and dropped them in a large ziplock filled with old tank water. Than I filled a plastic container with about 2-3 gallons of water. The rest went to the sink. When the tank had under 25% water left, I started to catch fish with a net. I put them in the plastic bin for transportation. It's the same bin I dropped 2-3 gal of old water in it. When I had all the fish in the bin, I started to catch shrimps. Those I put in a small bottle filled at 50% with tank water. When every one was in its transport container, I took off. The first thing I did at my new home was to drop the containers in the new tank just like I would have done if I had purchased the fish. While the water was matching temperature, I reinstalled my filter on the new tank. After about 20 min, I started to add water from the new tank in the container. I repeated the above step a couple of times and after that, I scooped the fish out of the container and put them in their new home. For the shrimp I removed the cap and let the bottle sink in the tank (I didn't mind ~500ml of old water in 75gal).

A couple of days before the move, I started to feed less. About 25% less by feeding and the two days before the move I didn't feed. When they were moved, I didn't feed the same day. But the next day I fed them lightly.

It's been over a month since the move and I didn't lose any fish. They are all going great. For the shrimp I can't say because it's too hard, but I still see plenty so at least a large portion survived.


I think Rolf has a pretty good idea, but I don't see why you have to haul them in the larger tank if it's going to be a problem. You could just get a Rubbermaid tote with a locking lid and transfer them all in that. You could even get some fish transport bags from your local fish dealer and put them in there, just like when you buy them. Either way, they're in 100% the water they're used to. With the Rubbermaid tote, you'd want it on the big side anyway. You don't want to fill them more than half or less with water so that moving doesn't slosh them around and out of the container.

You could also still use your 75gal you want to use. 15gal is 20% of 75gal. If you take a 25% water change out today and put it in the 75gal tank, then do so again in one week, you'll have ~7.5gal of 100% in the tank. Then in 2 weeks when you move, add the 15gal from the original tank. Maybe transfer half the water, then the animals, then the rest of the water. You should now have 22.5gal in the 75gal tank. This is 30% of the volume it can hold and is 7.5gal more room that they're used to.

I think that is a good amount of water in the tank for traveling and it's 100% the water they're used to. Also, if you felt it was a little low, you could even add in an additional 3.75gal of fresh water. That would be what they'd be getting in their 25% change anyway. I think you can easily get away with these figures. I know it's a little more of a change than the typical 20%, but most people usually guess on how much their taking out and I don't think it's a big enough difference to matter. Good luck.

  • I did the move this weekend finally. I fully filled the 75 with fresh water and waited 24h to get the fish in. I aclimated the fish just like i would had buy them. So far so good. 3 days later the are still all alive
    – Rémi
    Jun 21, 2016 at 23:59
  • Did you just fill it up with straight uncycled water or did you use water from your current fish tank?
    – Dalton
    Jun 22, 2016 at 13:35
  • Uncycled water with dechlorinator. Most of the bacteria live on hard surface anyway. I transfered the filter media in old tank water then put it back in the filter in the new tank
    – Rémi
    Jun 22, 2016 at 13:40

I did something very similar.


I starter by adding cycled water from my old tank to the new tank. After weekly transferring multiple buckets for three weeks, the new aquarium contained a lot of cycled water from the old aquarium (30%).

I also shared some filter material from the old tank with the new tank.


Then I started to empty the old tank into the new and bigger tank, scooped out the fish and finally transferred the last bit of cycled water.

The new tank was at this point filled with cycled water for about 55%.


I started by adding (non-cycled) water to new tank to further fill it to about 80%. A week later I added the last 20%.

All my livestock survived the transfer (Neon and Tetra species, some Cherry shrimp and Cory's).

  • Hey thanks for your answer, unfortunately, since I'm moving at the same time as the switch will occurs, transfering all the water will be pretty near impossible
    – Rémi
    May 22, 2016 at 21:37
  • Temporarily store water in buckets? You can buy them pretty cheap ;)
    – Rolf ツ
    May 22, 2016 at 21:53
  • Still I would need to do like 10x water change to have about 2/3 of old water in the new tank, it isn't really doable for me. I would need to store this water for about 2 weeks and it would fool itself or I would need to buy a couple of air pump to keep the water from stagnating and most of the bacteria are located in the filter and on the gravel/sand/plants. At this point I'm not so sure how I will do it. I will see if I can't at least transfert a couple gallon of old water.
    – Rémi
    May 23, 2016 at 18:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.