Changing filtration methods

[aic]

I've finally got my 40B to the end of the cycle and now I'm starting to have a change of heart.

I had originally planned on setting it up mostly for a QT tank, but now I've gotten the itch to get a new QT tank and stock this one. It's currently set up with a large HOB filter with sponge and bio-media and two RW-15s. Has live rock and sand.
I'm wanting to add a sump as I plan on using the tank. Do I need to be careful of adding a sump system to a freshly cycled tank? I'd leave the HOB filter on the system until completely stable.

[backdraft]

I have done something like this in the past. I just added the sump and the extra water and skipped the water change for a week. everything worked out fine for me.

[OldReefGuy]

yes, you can do that and should have no problems.

[AlSimmons]

+1

By adding a sump all your really doing is adding more water volume to the system. The same results can still be achieved with or without one though.

[ericarenee]

If you shut down the hob filter put its media in the sump . if you remove that you could have a mini cycle of sorts.. i am sure supporting bacteria is growing in there...

[CStrickland]

The only issue I see is that if it will be your display you might wish you drilled it. That's much easier on an empty tank. If I were you I'd probs fill up an old Rubbermaid tub with salt water, transfer the rocks into it and drain and drill the 40b and get it plumbed. You could maybe leave a few inches of water in the bottom to keep the sand wet with some plastic laid on the water surface to keep out dust and glass chips, or not and toss it in a bucket. Then put the rock back in and pour the new water back over it. It might take a day or three for your bacteria to restabilize but it won't set you back too far and you won't have to deal with hob overflows.

For your new QT, maybe reconsider the rocks and sand altogether. It's not necessary and a bit of a hassle.

[Mark9]

If you build your own sump, buy the proper silicone and let it cure a reasonable length of time. BRS sells reef safe silicone. I did not feel safe buying from Lowes.