I believe you posted on Amazon as well, where I answered this question. When a filter backflows, there is a clog somewhere. It can be the cartridge if overfeeding is occurring, or it can be that the filter has pulled debris into the motor region or the impeller. Unplug the filter, remove it from the tank, and take it apart. It may be a simple as hair wrapped around the impeller. This is a common issue and easily remedied with tweezers. Over time, other things like hard water buildup, algae, sludge, etc., can cause this issue, but I suspect you are either over feeding or some gravel grit is interfering with the impeller, something along these lines.
Date published: 2017-01-11