I would set up the 75G tank like you want with sand (Pool Filter Sand works best), decorations, and so on. Then fill it up with tap water of the right temperature and ad the required amount of dechlorinator. Then transfer the filters from the 45G to the 75G. Make sure everything runs as expected. Then transfer the fish.
You'll loose some bacteria from the old substrate, but that shouldn't even be measurable as ammonia spike. Most of the bacteria will be in the filters, and get transferred. Transferring water only transfers waste. Better to start with fresh water and let your filters deal only with the new fish poop in the new tank :wink:
If the 75G is going in the space of the 45G, you can break down the 45G first, and keep the fish in a plastic tote or buckets. They'll be fine for the few hours it might take to get the new tank perfect. Covering the tote with a towel or some such thing will reduce stress and prevent jumpers. An air pump would be good, but is not necessary if you don't have one. The bacteria in the filters wouldl also be fine during that period.
You'll loose some bacteria from the old substrate, but that shouldn't even be measurable as ammonia spike. Most of the bacteria will be in the filters, and get transferred. Transferring water only transfers waste. Better to start with fresh water and let your filters deal only with the new fish poop in the new tank :wink:
If the 75G is going in the space of the 45G, you can break down the 45G first, and keep the fish in a plastic tote or buckets. They'll be fine for the few hours it might take to get the new tank perfect. Covering the tote with a towel or some such thing will reduce stress and prevent jumpers. An air pump would be good, but is not necessary if you don't have one. The bacteria in the filters wouldl also be fine during that period.
