I just moved my 29g from one side of the house to another 2 weeks ago. it's FW
though. My setup was simple to begin with: no sumps or plumbing. Just wall hung stuff.
One thing is for sure: YOU NEED TO EMPTY OUT THE TANK. No 2 ways or shortcuts about it. Keep it real.
What I did was this: (it was in strict sequence!!)
1. siphoned water (skimming from the surface) into a 5G bucket. Then, I placed all my fish in there. I placed an airstone and a water heater. Then I covered the top of the bucket partially to prevent any harakiri jumping fish from executing suicide.
2. I took another 5G bucket which I conveniently have. I placed all my ornaments in there. Then used that as a "basket" to transfer the ornaments to a rinsed sink.
3. using the same second 5G bucket, I siphoned away the water, leaving only enough that covers the substrate in the fish tank.
4. guess what, I have another bucket that I placed the substrate in (including the small amount of water I left in the tank). Then emptied the tank totally.
5. Now that I emptied the tank, I disassembled all attachments (heater, filtration, air stones, what have you).
6. I removed the tank from the top of the stand.
7. I moved the stand to the new spot.
8. I ASSESSED THE NEW POSITION AESTHETICALLY!! ASKED FOR OPINION FROM MY FIANCEE. This is the most critical one. It's do or die.
9. Re-assemble the setup (stand, attachments and all)
10. Replaced the substrate and ornaments.
11. Poured 3/4 of my 5G bucket (the one with fish in) back to the tank. Keep the fish in the bucket!
12. Filled the tank with new water. Conditioned. Cichlid-salted or what have you. Made it run with filtration, air stones, powerheads etc for 20 minutes.
13. I then used a "trickle" tactic to slowly pour back water FROM THE TANK to the bucket. This is to re-acclimate the fish to the new water.
14. When the 5G bucket filled itself over time, I scooped the fish back to the tank and poured back water from the bucket to top off the tank. voila!
It's a long process but it was a success for me. No fish got stressed, there wasn't a mini-cycle that happened. Everybody is happy. But it took me 3 1/2 hours to do.
The lesson: If you don't want to do the above, keep it where it is. However, don't be misled by the "numbering" of the instructions above. IT WAS DARN EASY!! Good luck!