buckets
The fish can live quite a long time in buckets, you may need to heat them or even aerate them, but buckets work really well. Don't feed the fish for a few days before the move.
Plan plan plan but you'll need to do something like this. (I just did this, twice, over the Christmas break, since I was tearing down and resetting my 75 gallon tank.) I'm going to write out what I did, you'll need to do something different, maybe with buckets maybe with 2 moves.
The important thing is to keep your filter bacteria alive!
- Setup 65 gallon tank, build a temporary cinderblock stand, level, leak test.
- Transfer half the water from the 75 to the 65.
- Transfer heater and filter to the 65.
- Start catching fish. Realize that this really stirs up a lot of mulm and I can't see the fish
- Remove most of the water from the 75, remove all plants and driftwood, this all goes into the 65
- Catch all remaining fish
- Sleep
- Catch all remaining fish, yeah, some hid really well.
At this point I tore down the 75, cleaned, etc... which you won't have to do. Then I put it all back together. I got it done in 2 days but allocated 3 for it, just in case something went wrong.
I'm guessing you would do something like.
- Fish into buckets, keep all the water (might be optional, if you fish are used to huge water changes this shouldn't be an issue.)
- Preserve the filter bacteria, maybe run it off a buckte
- Drain the 96, remove it.
- Install the 300, substrate, plants
- Add the water you saved in step 1
- Add the filter, heater etc.. You probably have a new filter, so put the bio media from your old filter into the new filter.
- Add the fish
Plan it out. 300l is a big tank, think about what can go wrong. Is the new tank level? Can the floor handle the load? Did you leave room behind for hoses. One you have the gravel in it, even without water, you will likely
not be able to move it.
You've got this, you can do it!