I moved tanks across town couple of times now. Luckily you aren't moving across town, so it is a little easier. The larger challenge is that you want to set up the new tank in the old tanks position. The number one priority is your livestock - getting them moved and back into the tank as quickly as you are able. Time is essential here.
Firstly I was planning on using everything from my old tank as the Reefer has to go in the same place as the 250. Now is it going to be fine using all of my old live sand from the tank? As I have read that it could cause issues and possibly kill everything or start a cycle again and I don't want that. I could but a couple of bags of new live sand and then take some from the old tank to help seed it further.
I'd actually either get rid of the sand or set it aside to thoroughly clean before using it in the new tank. What I'd do with the sand depends on the state of the sand. Sometimes it isn't worth keeping.
Secondly I will have to add 100ltrs of extra water to the system which I can mix up the day before but will that cause any problems add that much new water to the system? As it is particularly a massive water change.
Having that additional water on hand would come in handy when filling the new tank up.
You can use the old water as long as it isn't stirred up. If I was making this move, I would save as much of the DT water as possible. Not only for the container that will hold your fish/critters, but also as backup water (this is unless the water is foul and unusable). I would first siphon the water from the upper part of the tank into those containers that you plan will hold the fish before the water gets fouled (the water will foul once you start to move rocks around). You can choose to lower the water in the DT to a 1/4, 1/2, or 2/3rds. I'd personally use about half the water. Then pull your inverts/fish/corals out and place them into the containers that have the tank water in them.
Then pull live rock out. You can use all the old rock in the new tank and I recommend that so that you aren't cycling a new tank. Sometimes it is hard to catch the fish with the rock in the tank and the rock will have to be transferred out while you are also catching the fish. Be careful of stirring up gunk off the bottom of the tank. Keep all your live rock in water while you take down the old tank and set up the new tank. You can keep the rock in with the fish if there is room. I've done this before.
I found it useful have two (or more depending on the size of your tank) of brute trash cans with ready to go salt water in them as a backup before you break down your tank. You never know what you will need the extra water for. And if you get an ammonia spike in the container with your fish, you will want to change out that water as soon as you can.
Thirdly is it a good idea to transfer over my old filter media and sponges and put them in the sump for the time being to help with the filtration?
You can use the old media as long as it is still good to use (i.e. not old). If it is old media and it is about time you would have changed it out in the old tank, then I wouldn't use it. If it is fairly new and still good, then it wouldn't hurt to use it for a couple of weeks in the new tank. I don't think I'd use the sponge, I'm not a big fan of sponge filtration in tanks.
I have a good idea about housing the fish and corals and rock temporally in massive bucket with a heater, air pump and air stone but was just the extra water, old sand and filter media transfer as I want to get it all right.
I've used ice chests (isolated) for live rocks/ corals/ inverts (w/heaters/air stones). Action Packers for wet tank equipment (waterproof and has a lid) and large plastic trash cans (Brute) for fish (w/heaters/air stones/pumps).
How long do you anticipate the fish being in the buckets? If you have them in there more then 24 hours I'd pick up an ammonia alert badge (or ammonia test kit) and have PRIME on hand just in case there is a spike in ammonia levels.
I wouldn't add the sand or media in the temporary container with the fish/critters.
Thanks! [emoji4]Would love to have the rsm 250 somewhere else whilst the tank cycled but I have to put the new tank in the exact place the old one is and I haven't got anywhere else to set up the old tank which is a pain.I don't think there is anything I can even add to the tank to stop a cycle as I think the first time I moved everything I had a small cycle but I have a lot more more fish and corals this time and I don't want to loose them.
In the newly set up tank that you moved your old tank into can have mini-cycles. If you used much of your old rock and water then the chances of a mini-cycle are lower. But if you used all new water with your old rock you may see a mini-cycle. And if you used new rock you will pretty much be cycling a new tank. By moving your rocks you are exposing them to air and disrupting some of your established bacteria. Keeping the rock in water as much as possible is key, don't let them dry out. Yes, much of the bacteria in center of the rock should be fine. But, since you are disrupting the rock anything that dies on the outside of the rock can lead to a cycle in your tank. Just watch your ammonia levels in the tank once it is set up and prepare to do large water changes if you see the levels rise.
I find that having these items on hand makes things easier: heavy duty gloves (moving rock); nets; heaters; pumps; siphon; buckets; containers for livestock/rocks. Items that clean up spilled water from the floor/carpet. Think about other items you may need. Have them all on hand at the beginning of this move.
Also before the move, think about what livestock you have, any special needs? What about your corals/snails/seastars/etc. Think about what you have and how you are going to store them; how long your will be storing them for; and how you are going to transfer them. What additional equipment are you going to want on hand: bags, rubber bands, styrofoam dividers, etc. Do any fish need to be separated or all together? If kept more then 24 hrs, how will you handle the ammonia spike?
Take time to run through the move in your mind. Make note of anything that you may need.
I think you can get it done over a weekend if well planned out.