I've had both before. The yoyos never had a powerhead in the tank, but I don't think they would have minded it, as long as is wasn't overpowering. The zebras were in a tank with powerheads, and seemed fine with it. I would say it's not necessary for either species, but neither would be especially bothered by it, as long as there are spots with less current, and their cave is in a calm section.