Is something wrong and other bits?

One of my Fluval 4 plus filters is every twenty seconds or so spewing out
loads of tiny air bubbles by the thousand, this has only just started
after
being ok for about a week.

There is a little knob ontop of the outlet you can twist to stop this as
bascially there is an inline air in-take on the outlet of the filter.

Geoff

Thanks very much for the info Geoff & Geezer.

--
Haynes'ey.