How do I refresh nagios and stay on the current page?

Rightclick the frame, reload frame

modify your template and put

<a href="#">refresh</a>

You can fix this by adding

header("Cache-Control: max-age=7200, public");

to the beginning of the PHP code section of share/index.php (NOT in the if-clause!).

Your browser does not know if it should cache the current frame, so defaults to not doing so. This causes it to reload to main.php instead. (Appreciated Source in German: https://checkmk.de/lw_nagios_frameset_f5.html)