Keep the water. Keep everything, just a bit of a time heavy exercise, I'm dreading having to move my 180l when I move house. I'm just getting it looking how I want it
I wouldn't worry too much about keeping the water if it isn't hugely different to the pH from your tap. As long as you test the water before hand to see what the levels are like, and then test again once refilled to make sure it's similar, and acclimatise accordingly. If it makes you feel a little bit less nervous, keep half if you can
I've moved tanks several times now both to different places in the same house and to totally different areas in the country. I didn't keep any water (more of a case that I couldn't when moving county), and just made sure to acclimatise properly before releasing the fish.
levels look good as well and what great fun that was getting the fish into the net the pleco just would not let go of the glass lol just to think got all this again when i upgrade to my 180l rio next year.
cheers for the replys