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Discussion Starter · #1 ·

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Fans are great and I have a single fan on my 15gal tank and it lowers the temp down to 23c, but at night you have to be careful as the temps can drop down to 19c, and the other bad thing is evaporation from the fan, so you have to add water at least 1-2 times a week. The temps over here in Japan get up to 35c indoors.
 

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Ryzi, I think that whole bank of fans may be overkill.
all you really need is one blowing across the water,
since it's really the evaporation that cools the water.
I have on 3" fan that lowers the temperature by 4°F.
keep in mind a fan may not make it cooler than ambient
room temperature, so if you have an 80°F room, you
won't get 76°F water, but if you have a 76°F room,
and the lights bring the water up to 82°F, that fan
should get the water down to a comfortable 78°F.

 

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A great, cheap way to control your tank temperature. It is widely and commonly used in Southeast Asia where planted tank may "boil" to over 33C.

The only drawback is excessive water evaporation, which is not a problem if you are doing weekly WC.

If you do not mind the evaporation and if you only need to lower temp just a few degree, this is the right way.
 

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Discussion Starter · #9 ·
Ryzi, I think that whole bank of fans may be overkill.
all you really need is one blowing across the water,
since it's really the evaporation that cools the water.
I have on 3" fan that lowers the temperature by 4°F.
keep in mind a fan may not make it cooler than ambient
room temperature, so if you have an 80°F room, you
won't get 76°F water, but if you have a 76°F room,
and the lights bring the water up to 82°F, that fan
should get the water down to a comfortable 78°F.


so the windchill of the air created by the fands wont lower the water temps below room temperature?
 

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so the windchill of the air created by the fands wont lower the water temps below room temperature?
in my experience, no.

"windchill" is a confusing term here.
we feel windchill on our skin because our sweat evaporates and the chill is because the very surface of our skin is so much colder as the moisture literally boils away thus drawing lots of heat from the skin surface than our bodies and the air around us. so in fact we are really at about the same core temperature, it's only the surface of our skin that feels a chill.
it's the same thing with the water surface of our fish tanks. the fan causes a chill at the water level by creating a low air pressure zone that's less than a millimeter deep, which is enough to release some of the excess heat built up in our water when compared to the ambient temperature of the room, but not enough to actually defeat all the heat from the room and light fixture radiating and migrating into the tank water through the glass. the net heat being boiled off by the fan may not be greater than all that heat still trying to migrate back into the water from the room.
so if you lined your entire tank with insulation foam, and left your fixture off, a fan will in fact lower the water temperature below ambient room temperature since the net heat boiled off by the fan will be greater than any heat trying to migrate back into the tank water from the room air.
 
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