I am in the Underwater Tempel and finished all i can do but in one room is a crate on the floor which leads i think to the Libary , i cant open the crate how can i open it ???

The only grate I remember is one with a lovely mermaid on top, who will open it for you if you ask her nicely about a number of subjects (not sure which one triggers the grate). The same one you get the 1st glowstone from. In case you killed her: I tried that once and could click on the grate to open it, although you must be careful not to stand on it while clicking.