Yes, platies need air pumps. Despite being very hardy, platies aren’t able to survive in low-oxygen environments. Oxygen levels in normal tank water are too low to sustain platies, so an air pump is needed to further oxygenate the water.
Air pumps create surface agitation that introduces breathable oxygen into the tank. You can also use an airstone or a bubbler to increase the oxygen levels in the tank.
Additionally, consider adding live plants and vegetation to the tank, as they help promote better oxygen exchange. Over time, you could develop a self-sustaining ecosystem that doesn’t need further oxygenation.