I have done this a number of times over the years. it is inportant to use the same substrate if possible. I normally do things this way.
1. I try to leave the fish in the original tank if I can. I leave the filters running. Then I remove the plants to a container with clean water. Next, I syphomn out the substrate abnd rtansfer it to the new tank. If I need more new substrate I want that to go in before the old. The old will hold some amount of good bacteria and this normalltt beeds to be lesss than an inch deep in terms of the bacteria being able to survice because it needs oxygen. This chabges when you have plants in the substrate. There can be bacteria deeper as some plants actually transport oxygen into the anaerobic area around roots to foster an environement were the nitrifying bacteria anc thrive.
Be sure to have new safe water available since siphoning out substrat does remove a lot of the water. You need to replace water to insure the fish will be doing OK. This replacement water needs to be dechlored if you use dechlor.
2. I want there to be some water in the new tank to insure the substrate stays wet. The next step is that I place the decor- wood, rocks etc. where they will go. This water needs to be dechlored if you use dechlor.
3. I add more water and begin to put the plants into the tank. My normal practice for planting a tank is to do it in 3 stages based on the height of the plants. 1st I do the shorter forgrount plants having raised the water level to where these plants will be submerged as I plant them.
4. Once the fore-gound is done I add more water so I can plant the mid-ground heoight stuff so it will be submerged as I do.
5. I then add enough water to plant the taller background height plants.
6. Now it is time to move over the filter or filters and heaters. Most of my tanks have at least 2 filters on them and they will have 2 heaters as well/ So I move the bigger filter over first and leave another on the old tank. I move one heater as well. Once I have the filter running on the new tank it is time to catch and move the fish. However, make sure the water temp in the new tank is in the proper range for the fish.
7. Once I have moved the fish I then move the second filter (if there is one) and the same with a second heater. What you should have at this stage is almost everything from the old tank moved into the new tank. You can add new plants and decor you want to add to the new tanks during the appror[pirate stage for doing so. What is left behind is a dirty old tank and you can dispose of it as you see fit.
8. Of course you should be moving things like thermometers and lights as well. You will need to have lights on both tanks for the move so you can see what you are doing. You may need to buy new lighting rither to add to what you have or to replace it with something stronger/bigger.
9. For a week or so after you make the transfer the tank should be safe for the fish but may not be. So, test ammonia twice a day to make sure. You may have some loss of bacterial capacity or you may not. Testing will tell you. I would not feed the fish for at least 24 hours before the move and not for 24 hours after. The more the fish breath and poop, the more of their ammonia creation capacity increases. Plus uneaten food can make ammonia as well. If you see no ammonia after the move you can start feeding the fish the next day.
Bear in mind that under optimal conditions the ammonia bacteria can double in about 8 hours and the noitrite ones more like 11 or 12. If you lose 1/4 lf the bacteria, reproduction will replce that loss in a few hours. So do not panic if you get some lower level readings. The toxiciyt of ammonia in water is based on the ph and temperature of the water. Higher means more toxic. Most test kits measure both forms of ammonia in water and it is the NH3 form that is highly toxic. if you are not familiar witrh how this works there is an excellent expalantion in the cycling article on this site.
Have a read of this rescue article:
https://www.fishforums.net/threads/rescuing-a-fish-in-cycle-gone-wild-part-il.433778/ There is a section in this article that deals with ammonia and the difference between NH3 (ammonia the gas) and NH4 (ammonium). The first is toxic at lower levels while the second is way less so.
If you get stuck on any of the above feel free to shoot me a site PM. I get email notifications for these but I do not track thread replies specifically. I am retired and online all the time so I will see the email notification for your PM.
