Planted Tank Obsessed
Join Date: Jul 2012
Location: Los Angeles, CA
I would drop the powerhead and just angle the spray bar slightly upwards so it agitates the water. Without knowjng the full history of the tank, I'd imagine the powerhead is what's spooking your cardinals. (A big black thing that makes tons of noise and shoots a high power water stream is probably dangerous looking to a small tetra like your cardinals.)
Upping your circulation to curb your algae sounds like a roundabout way of trying to maintain your tank. Try to fix the underlying issue that's causing the algae e.g. too much excess light, not enough co2, nutrient excess, etc. If you can tell us what kinds of algae you had problems with before, we might be able to help you troubleshoot the problem.
ADA 120P, DoAqua 90P, ADA 60P, ADA 30C x2, ADA 45P, ADA Mini-M