In addition to being higher than normal, 30-35 is a very large range. If your heater will not keep the tank at a more consistant temp I would recommend replacing it.
Are you heating the tank to those temps or do you live some place with high temps at this time of year? Higher temp. water holds less oxygen & can stress fish especially if overstocked. What is the tank size? It can help to create more surface movement by lowering the water level, adding a power head or having a fan blow over the surface.