A lot depends on the size of the fish and whether there are any ornaments in the tank that will block the current. In my case, the discus are 4.5 - 5.5" in diameter and it's a completely empty tank except for sponge filters on one end. I run a double wavemaker on one end of the 75 gal tank pointed slightly upward.

When the light comes on in the morning, the discus are usually at the end with the stronger current. During the day, the tend to congregate in the other half. Not sure what to make of that but these fish are definitely not fighting the current at night. I presume the current in their native habitat to be the same day or night, but have no idea if that's true.