Andy Sager
Aquarium Advice Addict
There will be no existing fish, this is a species tank. Not to be rude(and i mean that)but i dont need to know about QT. This is a question about cutting down the time the fish are bagged. Water changing 12hr before or when they arrive.
No offense taken. Just putting this out there as you obviously are dealing with a new situation. When you get fish shipped to you ( and I've shipped fish from the US to all over the world), pathogens within the fish can become "activated" and can infect your tank. These pathogens will now be in the tank for the duration and effect any new fish you put into the tank in the future unless you medicate the tank. This brings up a whole new set of issues. This is why I suggested the QT. Acclimating the new fish into this tank would be as usual. I've used drip and bag methods both depending on the situation.
As for getting the fish out of the bags quicker, quicker is not always better. If you are getting an ammonia reading and the PH is under 7.0, the ammonia is not toxic to the fish so the need to hurry is not there. If the PH is below 7 and you use an airstone in the opened bag ( or bucket if that's how you are acclimating) just make sure you don't put the fish under heavy aeration as this can cause the PH to rise which will then change the ammonia in the water to the more toxic form. You also need to be mindful of the water temp. The colder the water ( when the fish first arrive to you) the less air they need until they wake up. Gradually increase the air as they wake up and you get further into your acclimation.
As for whether to change water in your tank 12 hours or 1 hour before the fish go in, it should be changed before the fish go in. Shouldn't matter how long before. If there is no fish life in the tank now, doing the change now shouldn't be any different than doing it tomorrow. As previously stated however, the sooner you do it, the more time you have to see if there are any issues going on that your nitrates go up in an empty tank. That's the sign of a problem which your new fish shouldn't be exposed to.
Sorry for the long answer but there are a lot of variables to consider