Will it hurt my fish if I put aluminum decorations into my fish tank?

maybe
what if he/she starts sucking on the aluminum

most likely

Don't put aluminum in your tank.

Buy some aquarium sealant, and some river stones and make a cave out of them. It's fun and looks very natural.

i wouldn't do it. aluminum puts off micro eliments.

no it won't. i had fish you know when you put a new fish in? kinda like that. feel the excact same temprature and then let it sit for an hour if it's a baby (wich it is) you should wait till it gets bigger. no other fish i had lots of guppies and my brother had these black fish i don't remember the name then my guppies had babies and my brothers fish ate them i also had a chinese fighting fish but it passed away of old age and i had a cat fish. (one guppie and the catfish survived) .... wait till you're fish gets full size then you can