Pico Reef Temperature Control

A heater is essential for a pico reef. It will help keep your tiny volume of water from bottoming out to dangerously low temperatures and help keep your system at a stable temperature 24/7.

I keep my temperature between 79f-80f​. But anywhere between 76f and 82f should be fine. The key is being consistent with your temperature. Corals will adapt accordingly within this range.

Small temperature swings may be inevitable but should be minimized as much as possible.

A few degrees temperature change in a short period of time could wreak havoc on your corals and other life in your jar depending on what you’re keeping. Unstable conditions can cause stress, if not death, and the more likely you are to lose your tank. So, buy a heater.

There are many opinions on the size of heater you should buy. Personally, I like Brandon’s thought that you can never go too big. A big heater can definitely change the temperature quickly and keep it there versus a slow drawn out change which may end up frying your heater over extended use.

Heaters Reviews

Tetra Heater

While Tetra’s 78f preset heaters sound like an awesome idea, I’ve seen too many reviews and forum posts of these heaters failing and cooking their fish inside their tanks.

One reason could be that the heater needs to be placed in the water and left for a certain period of time before it’s plugged in and people are just tossing them in and plugging them in. I don’t know, but I certainly don’t want to accidentally plug it in and end up killing this precious jar of life.

Also, preset heaters can be finicky. Some will only adjust the temperature relative to the ambient temperature if it’s within a certain range. So if in the winter your room drops 10 degrees the heater might not be able to keep up.

I’d recommend passing on these types of heaters.

50w Rena Smart Aquarium Heater

Rena Smart Heater

I noticed this heater on sale at my LFS, so I bought it. It wasn’t as small as I thought it was going to be, but it was all black.

The reason it’s bigger is because it’s designed to hook up to some sort of overflow unit.

However, there is only ever a 0.4f temperature change between when the heater kicks on and when it turns off. Pretty good!

There are two big pluses about this heater:

  1. It’s plastic on the outside all the way around so it’s not prone to cracking like glass.
  2. It has a unique lighting system to notify you of problems. A flashing light means you need to check what’s going on because the temperature is out of range or something isn’t working. Whereas a solid light means it’s heating up.

I’ve used this for 3+ months and I’ve had no issues with it. However, I bought a Hydor 25w heater that is slightly smaller that I will use.

Again, if I had planned ahead I could have bought a heater off amazon that is much. So it’s great that you’ve decided to read my guides before jumping in with both feet and spending money you didn’t need to.

Hydor 25W Heater

hydor 25w heater

This heater works well and the brand has a good reputation. It’s a little bit bigger than I’d like but it’s still small enough to be hidden in my rock work. It’s smaller than the Rena heater mentioned above.

It’s fully submersible and made of glass so some care needs to be taken when putting in the rock work.

They don’t recommend having rocks actually touching the glass part of this thermometer to prevent hotspots which could lead to cracking.

So far I’ve had no issues.

I’ve only seen it come on for maybe 30 seconds at a time in the winter months and fluctuates the jars temperature by 0.8f which is still pretty good.

I’d recommend this heater for a 2 gallon jar or vase.


​To accurately measure the temperature inside your pico reef you will need a thermometer. Of course the smaller the better since there is limited space.

Those thermometers that stick on to the outside of the glass are not a accurate way of measuring temperature.​

You can buy a cheap floating glass thermometer, however these are not so accurate when trying to read them.

Temperature in our small pico reef tanks is very important. If you can’t tell if something is 82f or 84f, it could be a major problem.

A digital thermometer is the way to go. The cost of a digital thermometer is less than $10. I’m using a Zoomed Digital Thermometer that has a long wire with a probe. It’s low profile and easy to operate.

zoomed digital thermometer

Once your system is up and running you may want to remove this piece of equipment, but it's not a bad idea to keep it somewhere hidden in the back. Your heater might fail some day or you'll forget to plug something in after a water change. You'll want to be able to detect that quickly.​

  • February 16, 2016
Click Here to Leave a Comment Below 2 comments
Joao - March 23, 2016

Hey, first congratulations for your job! It’s really helpful!
So, I’m from Brazil, and I want built a reef jar, but I’m having a problem in how keep the temperature low, what do you recommend for me? I’m thinking in buy a small fan, I already have a temperature controller that activates a termostate to control temperature during the winter.

    reefjar - March 25, 2016

    Thanks so much!

    Tell me a bit more about your setup. Are you using an air line for circulation or a small power head? How big is your pico reef?

    If you’re using a power head, that will be the biggest problem. I would love to use one to keep my jar quiet but I can’t because it generates too much heat. Solve one problem, only to create another.

    The only solution I have found with using a powerhead is to use a MP-10 on one of the slower settings. But they are expensive compared to a simple air pump.

    I think you could use a fan, but I’m not sure how effective it would be if you just blow it on the glass and water isn’t able to evaporate.



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