Without a test kit that checks for ammonia, nitrite, nitrate, it's difficult to say if your filter is cycled or not. If on your test kit, you are showing any ammonia or nitrite, then you are not cycled. Showing nitrate only indicates you are cycled. Be careful with ammonia and nitrite and fish. They can burn fish's gills, and even cause death. I'm not familiar with your particular filter, but IMO any filter that uses cartridges suck. The reason is when you change cartridges, you lose what "good" bacteria you have in the cartridge. I would recommend you only rinse the cartridge in tank water, instead of replacing it. I recommend and only use Eheim Jager heaters. Some people will say this brand or that brand has kept my tank at this temp. for 6 months or 2 years, and that's fine. I have Jager heaters that are 20 years old, and still running on discus tanks. That's REAL quality. I would go with a Jager 250 watt. This heater would be very versatile. You could use it with on a larger tank in the future. Unlike other heaters, they can be calibrated. It's very easy to do, just follow the directions. Be sure to do this. It will insure the heater is working correctly.