when changing over to another tank, it's a good thing to take over the mature media but is it also a good thing to leave that tank running with fresh water for atleast a day, before adding fish? esp fry?

i was taught that in doing so, it will be safer for the fish. others use mature water, although, someone did say i was talking cr*p and that there is no such thing as mature water or that adding fish straight to a tank, without waiting is fine and no issue.

I've experienced mature media change over to a new tank and had to wait a few days for stats to level out.

am i talking rubbish?

swaping the media over is fine to a new tank just make sure the new water is dechlorinated or it will kill all the benificial bacteria.

the mature water thing is a a bit hit and miss as there is not enough bacteria in it to make it worth while the only thing is leaving it and allowing the chlorine to evap naturally on its own