How to limit comment indentations to one level?

This can be done, there is even a possibility to control this via the backend, just go to:

→ Settings → Discussion

And there under:

→ Other comment settings

You have the point:

→ Enable threaded (nested) comments | X | levels deep

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)