Temperature Issues

[Bronx19]

Hey guys, can the old mercury thermometers give inaccurate readings?
I have a Hydor heater that is suited for aquariums of 150-200L on a 100L tank, set to 30C. But the therm is only showing 28C. I have turned the heater up to 32C, and the temp only raises to 29C.

Granted the nights have been cold, I still thought a heater of this quality and size would do the job.

If the therm is correct, can I get away with keeping discus at 28C?

[jim from sydney]

you will find variations due to many things....your therm. may be placed well away from your heater hence it will pick-up the temp. at a different location... the glass area may be exposed to different temps also effected by the room surroundings...the latter is more evident in winter....as long as the heater works things should be fine...if in doubt take the heater and term. out and place in a bucket of water and test there..the volume is smaller and hence easier to check...you can expect marginal differences during the colder months....Jim

[Merrilyn]

Another thing to watch is, if you have the heater standing vertically, the column of heated water from the element will rise straight up to the thermostat placed at the top of the heater, and give a false reading.

I find it much more accurate to have the heater horizontal, or at least on an angle. It is then sensing the temperature of the surrounding water, and not just the water coming straight from the element.

[Fishpimpin73]

Another thing that you can do is up your circulation.

That has always worled for me.

At one time I had half a dozen therm in one tank just so I could make sure that the temp was constant :roll:

[Bronx19]

haha, thanks for the advice.

Ladyred: I too thought of that, I have had it placed horizontally on the bottom of the tank for a few days and it hasnt made any difference.

Jim: I took your advice and placed the heater into a small volume of water, it heated to 30 no worries.

In regards to circulation, I have a Ehiem 2222 and a sponge filter, both rated more than twice the tank volume.

So Im still puzzled as to why the thermostat placed at the bottom of the tank turns off, when clearly the water hasnt reached 30C according to the thermometer placed at the top of the tank.

[jim from sydney]

dont worry just check one against the other, as you did, and note the difference. keep this in mind..anyway once the heater is set it is fixed for all times i dont even look at my therm. i feel the glass and i tell you after a few times you can tell the temp, you will become an expert at this....Jim

[mistakes r crucial]

It could be the thermometer. I've recently thrown about 5 out the door (very cheap and nasty) as they would all give different readings and two of them were up to 3c out. Digital therms are a bit more expensive but I've found them to be spot on.
MAC

[goldenpigeon]

i dont really mess around with those cheap merc therms anymore. i find them to dodgy and a waist of time and money.

get a digital therm, they are way more accurate!