Help with fish tank water cooler project, parts and schematics

Hi all, as I live in Perth, the summer can get very hot here and as an aquarium owner my fish tank water temp is rising above optimal so I am wanting to start a little water cooling project using an Arduino and a few other parts. Screenshot attached.

I want to run a small pump that pulls water from the tank and runs it through a small radiator with a cpu fan to cool the water, then push the water back into the tank but i also want to run this with an Arduino hooked up to a temp sensor so that I can set it to turn on or off depending on if the water temp within the tank is to high or to low. Additionally a small digital readout of the current temp would be nice too.

I have a very very basic understanding of electronics but I love the learning process so i am looking for some help on what parts and how to wire this all up to make it work. Ideally i want to run all the power of the Arduino if possible but I am happy to hear everyones thoughts about how I can make this work!

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Hi Rueben,

Waterproof temperature sensors are easy to come by, DS18B20s are digital, meaning they’re quite accurate (1/4 of a degree) and fairly easy to use on an arduino:

As for the pump, you’ll definitely need a relay or MOSFET to control it from the Arduino, or maybe a small motor driver:

I’m not sure about pump choice, but we do have a few small ones designed for water features and the like:

When connecting it all up, make sure to use a common ground everywhere.

Keep in mind that this system can only cool down your fishtank to ambient air temperature, can you share more info about what temperature your tank gets to, and what temperature is acceptable? Is there a significant heat source in the tank?

Hi thanks for this, The tank currently sits at about 29-30 degrees and ideally i’d like to get this down to about 25 degrees. No head sources in the tank and away from direct sunlight.

Hi Reuben
As James pointed out, such a system as you have sketched can only cool to ambient temperature so if you have no heat source in the tank and I assume the tank is sitting in ambient temperature you will gain nothing.

For a fan to cool it has to get the air to evaporate moisture which would probably mean some sort of a small cooling tower arrangement. But as you have sketched you will not cool the water in the tank at all.

Think of the old meat cooling safes or the old canvas water bags hanging off the front of a vehicle. All are evaporating water off the surface of the bag or in the case of the safe the hessian on the sides. This makes the contents very cold and the hotter and the drier the outside temp the colder will be the inside of the container.
Cheers Bob


Hi Rueben
Add on:
This all boils down to the fact you are going to have to cool the air that blows over the radiator to cool the tank water.
It may be easier to get a small evaporative cooler or small portable air conditioner and blow it on the fish tank. Use an Arduino to switch that on and off if required.
bear in mind an evaporative cooler will not work in high humidity situations. Example they are not much good in Sydney during summer but work very well out in the country away from the sea.
Cheers Bob