Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Here are a couple of ways to assess the water flow.
1) How many gallons per hour is your filter rated for? I aim for 10x the tank volume based on the manufacturer's rating. This is often wrong, but at least it is a starting place.
For a lightly stocked, calm water tank, about 5x is enough.
2) Get a stick or dowel that is a bit longer than the tank is deep. Tie several threads to the dowel, perhaps 6" apart. Let a few inches hang down at each location.
Put the dowel into the tank in several locations and see what the thread does. It should wave some (low flow) or a lot (high flow).
If you use more than one piece of equipment (filter, air bubbler, powerhead) to increase the flow, make sure they all work together to make the water flow the same way. Do not set them up to churn or blend the water, or work at cross purposes to each other. You can test this with the thread on the stick, too.