There’s quite a list of equipment to purchase when a marine aquarium is being set up and keeping a marine aquarium can’t be called the cheapest hobby on earth.
However beginning aquarists usually follow the guidelines carefully, ensuring the size of this and the capacity of that is adequate. After all, buying a cheap or undersized item is not going to save money in the long or even the medium term. An adequate replacement could be required so economies at the beginning require caution.
Equipment nowadays is generally very reliable though there is always the chance of failure and so it is with a heater. Most marine aquariums run on one heater which includes a built in thermostat. The recommendation is for two, each heater being one half, or close to one half the amount of the required wattage. Two are recommended as if one fails then hopefully the aquarist will notice the problem before serious consequences arise. The heater(s) have a built in thermostat which is normally set at between 75 and 80 deg F (if there are two heaters they have the same setting).
There are variations of course. On my system there are two thermostat controlled heaters which are connected to an exterior thermostat. The exterior controlling thermostat detects the seawater temperature through a sensor and reacts to changes by applying more or less heat. The thermostat continuously pulses power through the other two immersed heaters increasing or decreasing the length of the pulse as required. In this way the seawater temperature is kept very steady. The exterior thermostat is set to 77 deg F. The two submersed heaters have their thermostats set at 80deg F. Therefore if the external thermostat stuck in the ‘on’ position the seawater temperature would rise to 80 and turn off protecting the livestock. If the thermostat totally failed… it would have to be noticed!
So, this external thermostat sat there for over eight years with the indicator light pulse always very regular. As with other equipment, a visual check was made from time to time, no problem, the electronics are brilliant! It becomes normal, ‘nothing wrong’.
But, one day, the temperature had risen for no obvious reason. This was noticed on the internal thermometer on the viewing glass. It was immediately assumed that some external influence was at work, after all the indicator light was still happily blinking on and off.
The seawater temperature however continued to rise so the adjustment knob was moved to zero. Still the external thermostat was not suspected. At zero the light stopped blinking as it should. It was turned on again and the temperature set to normal. After a while, the temperature was clearly slowly rising. Still not understanding, a reliable mercury thermometer was placed in the seawater to check the internal one which could have failed. Same result, rising temperature.
At this point the exterior thermostat did become suspect. The adjustment knob was moved to normal and the indicator blinked as usual. The knob was moved to a lower setting and the length of the pulses increased! The sensor was clean and undamaged. At last it was clear the external thermostat was at fault.
Lying in a closet was a heater/stat which had never been used, pretty obvious looking at some dust and the still coiled wire. The thermostat had been set at 77 deg F. It was a very simple matter to unplug the exterior thermostat, hang the back-up heater in the corner of the aquarium and plug it in. The temperature was monitored more regularly than normal but all was ok.
Has this put me off external electronic thermostats? No. The unit lasted as said over eight years in continuous use. It didn’t cost that much and I now have a replacement of the same type and make.
As the temperature was rising why didn’t I leave it to cut off at 80? I’ve had my fish and corals a long time (the fish with me the longest is a flame angel (Centropyge loriculus), eleven years. The corals mainly are longer than that). I didn’t want to expose them to any potential stress at all even though 80 is not usually a lethal level. Thank goodness the temperature didn’t go unnoticed if it was falling.
So there we are, a piece of equipment that for most of the time had been superfluous to requirements. I was so pleased that I had it.
When the overall cost of setting up a marine aquarium is considered adding a back-up heater isn’t so bad. Then of course there’s the lives of the livestock.