How long can I do this for?

[Rubasu]

I need to put everything from my 40B into a 20H while I update my 40 with an overflow and a sump...

Can I just put the rock and fish into the 20 with a few power heads and a heater? Or will I need to go get a cheap hob filter as well? It will be for about a month or two.

 

[flooddc]

I think it should be fine with HOB filter.
Since you're going to update the 40 breeder, IMO, why not get a brand new 40 breeder instead. It's only $40 more. Transfer everything over once done and have a spare 40 or sell it. less stress for you and the live stock.

 

[Reef Frog]

You'll need a light to keep the corals going. I'd run the power heads & the HOB because I'd probably run some carbon considering there is no skimmer. Extra water changes may be needed.

Assuming the fish aren't too big or active for the temporary setup, your corals get what they need (light) and you can maintain water quality, you could keep them in a holding tank indefinitely. We routinely keep fish in very small QT tanks for 5 weeks, sometimes more.

 

[Rubasu]

I was going to get a new 40B, but I have to take this one down while we get carpet anyway, so I'm just going to use this one.

Yeah, all of the fish are 2" or less - So nothing too big for the 20. I guess I have to run to petco and grab a cheap hob filter. Thanks!