Hi! I've been using the Oase Biomaster 350 for around 2-3 months now for my 96L aquarium. At first the pump was strong and flows well. But recently the outflow and inflow (with surface skimmer) has been really weak and inconsistent. It could be strong and I unplug it to feed my fishes and plug it back in and it would be weak. I clean the pre-filters every week but the flow is still weak. Any ideas on what is going on or tips to boost the flow and pump power of the filter?