Fluval 305 - Output Flow Varies

[Doogz]

I've had my Fluval 305 up and running for a while now, media consists of sponge, biomax and a bit more sponge, cleaned every 2 weeks.

Problem is every 10 mins or so the output flow drops noticeably. Around 30 seconds later it returns to full flow. No audible change to the motor just the sound of the water breaking the surface.

Water quality is excellent, only a small amount of nitrate and I'm using a sand substrate.

Does anyone have any ideas what could be causing this?

Thanks

 

[fishprotector]

Have you cleaned the impellor? It sounds like something is creating too much friction and causing it to stick.