Upgrading Tank, And Have To Transfer All Fish At Once

Not sure exactly where this belongs so I put it here.
So I am going to upgrade my overstocked 40 to a 75, but I don't have the space or anything to run both of those tanks in order to gradually transfer all the fish. I have a filter for up to a 75 on my 40 so I can move it over to the bigger tank no problem except that would then leave the 40 unfiltered and with just some airstones. I plan on putting all deco into the 75 and the water from the 40 into it as well. I'm just really confused on what to do with this situation. Is it bad to transfer everything at once? What should I do?

 

If you plan to take down the 40g, then you can just move the filter and the fish all at one time.

It would be no different than adding an extra 35 gallons of water to their current tank. The bioload is the same regardless of tank size. Your filter is cycled for the current stock. So moving them all at once is just fine.

Unless you wanted to keep the 40 running too....

 

That's what I was thinking, but I've heard it's not the best to move everything at once. I never heard an exact reason, it's just what I've heard.
The 40 will be kept running, except I'm planning on using it to move my mbunas from their grow out tank.

 

That's what I was thinking, but I've heard it's not the best to move everything at once. I never heard an exact reason, it's just what I've heard.
The 40 will be kept running, except I'm planning on using it to move my mbunas from their grow out tank.

So what will you do about the 40 gallon if you are taking it's filter to the new tank? Do you have another cycled filter?

You might be thinking of people saying it is not good to add too many NEW fish at once. But these are not new fish and the filter has been cycled to handle the bioload of your these fish. Now if you wanted to add an additional bunch of fish at once, then you would create a problem while the filter catches up to the additional bioload.

In closing, adding too many NEW fish to a tank at one time is bad. Moving all of the current fish and their current filter to a bigger tank at once is not bad.

 

The mbuna grow out tank has a Top Fin 40 and an Aqueon 30 so I will be moving those to the 40 since I don't plan on using the 20 high grow out for anything else, but I suppose I could take one of those back to the 20 if I need to.

 

Yep sounds good. So just move the filters and the fish to the new tanks. Make sure to test daily for the first week or so, but there shouldn't be too much of a blurp in the cycle when you're moving fish with the filter used to cycle their waste.