Hi Cassandra,First I hope the second tank is already cicled.Make sure all the parameters on the second tank are OK.
Because moving fish is a stressful ordeal make sure you use some type of stress solution.Then get a med to large container depending on the number and size of fish,pour some of the "old"tank water inside the container,add some floating plants to make the fish feel a sense of security,dont forget the water stress solution and then add the fish.
I usually try to do this without any bright light around the room,I honesty think this help the fish to be a bit more relaxed and less stressed out.
Now,start adding some of the second tank water.Use a cup or another smaller container,remember that the amount of water being added depends on a few things.If you have little water inside this container to begin with, you MUST make increments very slowly and in small portions.If you have a bit more water in the container then,add a bit more water from the second tank.
Another thing I forgot,make sure that this container with the fish inside is next to the their new aquarium.Reason being......To avoid having different temperatures inside the container and the tank.
I would say add new water every 15 minutes or so.I would stop adding water when the amount I started with is only 10% or less of the water inside the container.I know this could seem a bit lenghty but,at the end it will pay off.
How many times have you taken a seemingly healthy fish home just to die either the next or in few days?The mayority of this can be avoided by following my advice.I dont claim to be a "guru" of know how but,I know a few things or so,and how to acclimatize fish I do know.
A year ago I bought these fish from Aquabid .Really expensive little fish($25. per two pairs of gups,plus $20. shipping)I lost them all withing a week.I emailed the breeder and she told me how to acclimatized them,and ever since I never had any problems.
This also works with fish bought at your LFS.Please DO NOT put the bag with the fish inside your fish tank and make a hole.Remember....You dont know if the tank where you got your fish from had some sort of fungus or bacteria that could contaminate your healthy tank.Beside by using my method,your fish will have more time to get used to their new environment.
Well....Hopefully this helps you or anybody else making water changes or transferring fish from one tank to the other.If you have further questions let me know,I am usually patroling this forum.