Upgrading 20 Gallon to 40 Gallon. How to keep cycle intact?

[Troy328]

Hello all, trying to get some second opinions!

I currently have a 20 gallon tank with 8 cherry barbs and 2 kuhli loaches. (The kuhlis are the last two survivors out of a group of 10, I know I need more.) I'm planning on upgrading the inhabitants to a 40 gallon so that I can up the number of Kuhlis back to 10-20, and then also add more Cherry Barbs and/or another group of small fish alongside the Cherry Barbs further down the line.

The new 40 gallon tank is currently filled with water and substrate, has four new plants, and a new filter that is running. All that's missing is a heater and a cycle! And that's where my question comes in.

Will moving all of my old filter media from the 20 gallon's filter into the 40 gallon's filter ""instantly"" cycle the 40 gallon? (They are both hang on back filters with customized media, mostly seachem matrix in both) I have heard that transferring media from an established tank filter to a new tank filter cycles everything extremely quickly, or relatively instantly. Is this true?

I once moved my tank from one house to another, broke down the tank entirely to move it, and my cycle never took a hit after I set it back up the same day, so I imagine this is theoretically much less invasive than that and my cycle should be fine, yeah? Or was that just luck?

My concern is that 8 cherry barbs and 2 Kuhlis is a pretty low bioload for a 40 gallon. I'm worried that it might not be enough to keep the cycle going without it crashing, if that makes sense? Especially with new plants sucking up nutirents as well? I don't know if my reasoning works, but I'm thinking that taking the same bioload but then diluted across twice the amount of water might not support the bacterial colony living in the media, which would lead to a significant die-off, and then later a subsequent ammonia spike? Or that the plants might take up the available nutrients before the bacteria has a chance and then the bacteria starves? I suppose it could also work the other way around, it could be a good thing that the bioload is so low, with potential ammonia spread across a larger volume of water, the bacteria has more time and space to grow and absorb it? Or maybe the bacteria absorbs it faster than the new plants do, meaning the bacteria survives and the cycle stays intact?

I'm not sure which is correct. I suppose I could also just separately cycle the new tank from scratch, but that feels like a waste of good established media, and frankly, nobody likes that waiting part!! I'll do it if I have to, though 😅 What would be your approach here? Anyone have experience keeping a cycle intact when moving fish from a smaller tank to a bigger tank?

[Lennie]

On 8/4/2024 at 10:45 PM, Troy328 said:

Will moving all of my old filter media from the 20 gallon's filter into the 40 gallon's filter ""instantly"" cycle the 40 gallon?

yes it should as long as you don't add something that increases ammonia reading in a new setup like aquasoils

 

You can let the tank settle, blurry look go away, and directly move your filter media into the new one and move your fish

And in the following weeks, by keeping your parameters under control, you can add new fish slowly

[Tlindsey]

On 8/4/2024 at 3:45 PM, Troy328 said:

Hello all, trying to get some second opinions!

I currently have a 20 gallon tank with 8 cherry barbs and 2 kuhli loaches. (The kuhlis are the last two survivors out of a group of 10, I know I need more.) I'm planning on upgrading the inhabitants to a 40 gallon so that I can up the number of Kuhlis back to 10-20, and then also add more Cherry Barbs and/or another group of small fish alongside the Cherry Barbs further down the line.

The new 40 gallon tank is currently filled with water and substrate, has four new plants, and a new filter that is running. All that's missing is a heater and a cycle! And that's where my question comes in.

Will moving all of my old filter media from the 20 gallon's filter into the 40 gallon's filter ""instantly"" cycle the 40 gallon? (They are both hang on back filters with customized media, mostly seachem matrix in both) I have heard that transferring media from an established tank filter to a new tank filter cycles everything extremely quickly, or relatively instantly. Is this true?

I once moved my tank from one house to another, broke down the tank entirely to move it, and my cycle never took a hit after I set it back up the same day, so I imagine this is theoretically much less invasive than that and my cycle should be fine, yeah? Or was that just luck?

My concern is that 8 cherry barbs and 2 Kuhlis is a pretty low bioload for a 40 gallon. I'm worried that it might not be enough to keep the cycle going without it crashing, if that makes sense? Especially with new plants sucking up nutirents as well? I don't know if my reasoning works, but I'm thinking that taking the same bioload but then diluted across twice the amount of water might not support the bacterial colony living in the media, which would lead to a significant die-off, and then later a subsequent ammonia spike? Or that the plants might take up the available nutrients before the bacteria has a chance and then the bacteria starves? I suppose it could also work the other way around, it could be a good thing that the bioload is so low, with potential ammonia spread across a larger volume of water, the bacteria has more time and space to grow and absorb it? Or maybe the bacteria absorbs it faster than the new plants do, meaning the bacteria survives and the cycle stays intact?

I'm not sure which is correct. I suppose I could also just separately cycle the new tank from scratch, but that feels like a waste of good established media, and frankly, nobody likes that waiting part!! I'll do it if I have to, though 😅 What would be your approach here? Anyone have experience keeping a cycle intact when moving fish from a smaller tank to a bigger tank?

Whenever I upgrade I transfer all biomedia to or the filter and media to new aquarium. Sometimes a Jumpstart depending on bioload as stated by @Lennie.

[tolstoy21]

On 8/4/2024 at 3:45 PM, Troy328 said:

Will moving all of my old filter media from the 20 gallon's filter into the 40 gallon's filter ""instantly"" cycle the 40 gallon?

Yup. I do this quite a lot. You should have no problems.

If you are moving plants over from the 20g, those will also bring over beneficial bacteria.

Edited August 5 by tolstoy21

[DallasCowboys16]

If you bring all the filter media and a good amount of the same hardscape/plants from the old setup you will basically be instantly cycled. This will hold even truer if you use all the substrate from the old tank.

You will be golden.

[lefty o]

forget the cycle nonsense. you have beneficial bacteria, you move them over to the new tank on the substrate/plants/hardscape, etc, and you will be exactly where you were just now with more water. it will be fine, just dont dump 20 new fish in on day 1.