A couple of solutions in case raising the water level does not work:
Reducing the flow by diverting it with a plastic water bottle...
Filter Currents: A Betta's Worst Nightmare
Build a lip extension...
Here are some pics for the lip extension for the AC50 ( though it can be applied to most any HOB
). You'll need sturdy scissors, pliers, and optionally some form of heat (hot water or a hair dryer). Most LFS
sell the plastic strip separately in the lighting supply section. Hopefully the pics are self explanatory. You cut the strip to the width of the HOB
spillway. You want to make two bends (the heat helps make the plastic more pliable):
#1. Bend the section of the strip that has the part that grips the glass hood downward about 45 degrees
#2. Bend the strip lengthwise along the middle about 45 degrees upward
Next, use pliers to pinch the part that grips the glass hood in one or two areas. Do not apply too much force. This will allow the lip extension to grip the HOB
spillway and not fall into your tank.
You will have to adjust the bends and see what works best with your water level.