| Be interesting to see a pump set up at one end of your 90 gallon with bubbles to visualize the flow. Then have a movable baffle in side the tank that could be brought closer to the pump to show the effect to overall flow in smaller size tanks.
You could get a piece of rock with some wool or streamers attached at points around it and on the glass of the tank. And set up the pump to point at the rock or over the rock, along the surface, etc. and then look at the flow produced on the rocks surface. Be interesting so see what method produced the fewest dead spots. | 
