So yesterday I started heating my tank which is only filled with RODI water yet. I started heating more than 24 hours ago but the tank only gained 2 degrees. It's a 200L (53g) tank and I use the eheim thermo control 150 Watt. Should be fine for tanks 200-300L (53-79g). It also seems to keep hanging at 21-22 degrees celcius now and doesnt go up anymore. Is my heater broken or just not enough capacity?