Why do fish need to be brought into room temp water?

Because the water that they came from was room temp, the water in the bag is room temp and if you drop a fish in different temp water you could shock it and kill it.

but isn’t any temperature in a room make it room temperature?

@jamielynn2328 You have the correct answer.

You should really wait longer than that so the water has time to cycle and have beneficial bacteria in the water.

Please please, if you actually care about this fish, dont put it anything extremely small. It seems to be commonly accepted that this is ok. Its not.

It makes them viscous faster, so they can rip the other fish in you aquarium to bits more quickly,

You add the bag to your tank , wait 10 minutes – 30 minutes for the water to get to the same temp as the tanks . This way its not a huge shock on the fish , the fish won’t start to display signs of illness and loss all its finage and colour / luster . When ever i added new fish i NEVER waited 24 hours nor was i told this , it was always max of 30 minutes is needed . Little tip : if any fresh water fish you have in your tank get white spot or other spots , dip them in salted water it kills the disease and your fish aren’t bothered too much by it . I had to do it ( not to my fish ) and those fish are still alive today

@sandystrachan the 24 hours was for the newly set up tank, not the betta.

i have never heard of giving a freshwater fish a saltwater dip. Its a pretty common practice to freshwater dip salt fish, but ive never done the inverse. Ive always just treated the water with some sort of medication or if the parasites were large like fluke, manually removed them.

@uberbatman I hated using medications , and the salt dip works faster .
Did you know mollies can survive in salt water set ups , you have to slowly adjust them to the salt conditions. I helped someone with that before , they were going to flush the mollies in favour for salty fishes until i told them to slowly adjust them to the salt conditions . Black mollies .

@sandystrachan i actually have 2 mollies in my reef tank right now, so yes i did :P
they’re very good at getting algae off the rocks

most live bearers can make the conversion over to salt