Bought one of these heaters recently, as I'm building a small planted setup. Figured the space I save would be good.
The tank it's used on is a AQ-World Panorama 12. That's a 12L bow front aquarium. I figured once I account for all the gravel I put into it, plants, etc, the total water volume will be under 10L, so the Marina C10 (rated for 10L max) should be fine.
Now I've had it running for 2 days. The heater hasn't turned off at all (I can see the little light on it is on 24/7) and the temperature of the tank won't come up. When I close the doors to the room (small room) and run my heater, the temperature starts coming up to 24 (I have verified by using two different digital aqua one thermometers and one stick-on gauge that the temperature readout is correct). The highest I've ever seen it is 24.5° C. I've ensured good circulation in the aquarium etc but it just doesn't seem to be working.
I just got home from work ant it was sitting at 20.4° C. What's the story? Is this heater simply too small for this tank? It's apparently rated for 10L tanks though, so it should be fine shouldn't it?
At the same time I have a 40L tank running with a 50W heater and it seems to have no problems maintaining temps,.