luvbigfish;4717393; said:that hole is made for an airline to inject air into the water stream as bubbles , it will decrease the flow of water , I actually capped mine with an expandable foam earplug used in factories for hearing protection , squeese it and stick it in , it will expand and seal the hole , not too deep though
When you see water gushing out of a powerhead, that means a lot of force is coming out. When the water is standing still, the powerhead is weaker. This is not rocket science.
When I put an airline tube on the hole uncapped, water gushes out rather than the water standing still without an airline tube.