There’s a number of simple variables which you need to monitor and keep consistent when you’re looking after tropical fish. Water quality (e.g. nitrates), light and temperature. The last should be really easy to do, a heater with a thermostat on right?

But this does not appear to be the case. I bought a Superfish tank and it came with a heater, but I spotted that my fish were infected with white spot and wondered what was stressing them out.

I’d already replaced the light and I test the water regularly. I had a basic alcohol thermometer on the tank but it was pretty hard to read unless you were close up. It looked like the temperature was yo-yo-ing but it was hard to tell. I replaced the analogue thermometer with an accurate digital one (to one decimal point). This confirmed that the temperature of the tank was changing a lot more than it should of.

I went to my local fish shop and asked for the most expensive heater they had. This was the Sera Aquarium Heater and Thermostat 200W. It cost me 30 quid (which was actually cheaper than the Fluval one I was looking at at £40).

At first, I thought it looked pretty cheap and nasty, but when I got it out of the box and had a play and installed it in the tank it is really solid. The means by which you change the temperature is also solid and the temperature you’re aiming for is inside the thermometer so it can’t be rubbed off.

There’s a plastic guard to stop the fish from getting burnt if they get too close but what struck me the most was the clunk the thing made when it went on. It sounded reassuring. The light it uses to show the heater is active is also on the front the heater so it’s easy to see (unlike the Superfish one which I had to check the reflection to see if it was on).

Here’s a video of the Sera Aquarium Heater and thermostat 200W. It’s the box and then in situ in the tank. You can make out the thermometer I used on the table and you can see the orange light is on in the tank so it’s operating.

Here I’ve got the 200W Sera Heater and Thermostat next to the 100 litre tank I’ve installed it in.

Below is the graph I plotted based on taking the temperature reading for each of the heaters. These were taken on separate days in the same tank with the same thermometer. The Sera heater was set to 28 degrees (as I needed to increase the tank temperature) the Superfish was set to about 25 degrees (the scale on the top of the device has rubbed off).

As you can see the Sera heater kept a very consistent temperature whereas the Superfish one was significantly out. This actually got a lot worse in the evening and it shot up to 29 degrees which is what prompted me to change it. The Sera Aquarium Heater and thermostat only varied by 0.2 degrees C.

The other advantage to the Sera Aquarium heater and thermostat is the 5 year guarantee.