Tuesday, June 11, 2013

Keep fish, they said. It will be fun, they said.

I keep tropical fish, which have a fairly narrow range of temperature comfort.


In this part of the world, that means a tank heater.  This is not a bad thing, because a heater is $70.  You suction cup it to the glass inside in a high-flow water area, set the thermostat dial to what you think is about right, plug it in, and rack off for a couple of hours.  You then return and check against your tank thermometer, tweak as required, and you’re all good.


Because of the temperature sensitivity of the animals, I do keep a fairly close eye on the tank temperature, so when I saw it 2° high last week, I turned the thermostat down a little.  And a little more.  And a little more.  When you’ve finally got a tank 4° high and the thermostat is set 10° below that at absolute minimum and the heater still shows as running, a man does have to reluctantly admit to himself that he has a buggered thermostat and a new one will have to be purchased.


I installed a new heater on Friday last week and all was good until yesterday morning.  Tank temp a little low, but the LED showed the thermostat had cut in, so all good.  A couple of hours later, the temp is still dropping.  Checked the new heater and it’s got condensation inside the thermostat and about 2” of water inside the heating element, which is not good when you consider the bloody thing is a fully submerged 240v device.


Of course, by this time it’s 6pm on a public holiday Monday, I don’t have a spare heater, Calley is away, and I have to go to night shift in a little over 3 hours.  The tank will settle to room temperature over night, well below fish tolerance zone.




Some frantic maths shows that to heat 1 litre of water by 1°C you need around 4,180 joules of energy.  To heat 120 litres, you need  little over 500,000 joules, which is turn around 140Wh.  A 200W heater should therefore raise the temperature of the tank 1°C per hour if running continuously.


I extracted last week’s failed heater from the bin and trialled this, and lo and behold my maths is correct.  A simple 240v timer switch set to ‘blip’ the heater on and off overnight saved the day.


I now have a bloody expensive Eheim Jager heater installed, and if that fails I am going to be seriously pissed.

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