How do you know what decorations are safe to put in a tank?

I don't know if this is the right spot for this question, but.....

I like to put different things in my tanks. I have one in the Family room/Play room that had huge Legos in it and some other toys. I figured they were safe since the kids could eat them. The fish (huge pacus) ate on them as well, and they are just bigger.

I realize this is not everyone's taste, but, I am wanting to put old tea pots and china in a tank I am putting in my Living room. Teapots will make great caves and they have no sharp edges. I have done it on a smaller scale and I loved it.

Thing is I would like to put some other items in a new tank I am working on. I do not know what it may do to the water. Like crystal? Also some colored glass, maybe a mirror, what about metals?

Anyone have ideas on how to know what would be safe, or ways to make it safe would be great.

This is a tank that I plan to put Fronts, Clown Loaches, Angels, and an ornery red tail shark. I also would like to put live plants in it.

do not put anything metal in your tanks but pottery is fine and wood stuff falls off or rots but if the china has any kind of inlay in it i wouldnt put that in your tank just be careful with what you put in there