My #1 peeve in this hobby is aquarium heaters. That said, some fish just need to be warmer and it’s a necessary evil. This DIY journey began after losing two heaters over the course of three months on my 3 gallon nano reef. The first was fairly uneventful, as it just stopped working and the livestock didn’t show any signs of even noticing. The second, well, not so much. I came home one evening and could feel the heat radiating from the tank at three feet away, the thermometer read 114°F and my heart sank. I lost every living thing in that glass box and that was the precise moment when I was DONE with standard hobby heaters.

So wait. But you just said some fish need heat. Yup. They do. And if you can’t control the temperature of the whole room you have to do it for the individual tanks. But I’m here, friends, to tell you there are other options.

The main issue with typical aquarium heaters is that the internals fail, rendering the calibration off or unit unable to properly gauge temperature or regulate the heat. RELATED: NEVER, EVER, EVER BUY A USED HEATER. LIKE, EVER. So how does one get around that? External control, darlings. Now note, there are a few manufacturers who do offer an externally controlled heater. I have no experience with them, as the price point was generally out of my range, but may be perfectly good alternatives. You do you.

After some trial and error, a clear winner arose. While still using a standard heater inside the aquarium, all it needs to do is heat. No smarts involved. The little gem we found is an external digital controller box, and tiny probe that I typically place alongside the filter intake pipe making it practically unnoticeable. The magic comes from complete control of the temperature, set to a variable range of your choosing (I typically set it for +/- 2°, but you can go as OCD as tenth of degrees). Now, instead of the heater controlling itself when to cycle on and off it’s getting power from the controller box. Crank your heater up to high, plug it into your controller box, and let it roll. A little dot will illuminate when the heater is on, and the digital display is always on for a quick glance at the temperature. Pro Tip–install a simple toggle switch on the face of the display just under the digital read out so you can just switch off for waterchanges and not have to rummage through your stand to find the heater plug. You know what I’m talking about.

I’m sold. Where can I find this contraption?  Honestly, we’ve sourced all of ours from eBay. There’s two versions, one that needs to be hardwired and the other has an outlet and plug. We do the hardwired version here, sorta. David wires up a female connector to the box so that it’s still easy to plug in a heater (maybe some day you’ll want to use a different one, then you won’t have to cut another cord end off to splice in line). You’ll also need to wire the controller to a cord so you can plug it into the wall. A three-prong is the safer option, we’re talking about electricity here. But other than that you can use pretty much anything. If you’ve got an old appliance that’s broken you can even cut the cord and use that. The other version I don’t personally care for as much because the outlet is on the face, under the display. I mount my boxes in the upper front of the cabinets just behind the door so that they’re easy to view with a quick pop open. With a plug on the front I wouldn’t be able to do that, but there’s no reason why YOU can’t, or shouldn’t, if that mounting option isn’t paramount to you. Do make sure the controller is for 100V (220V for our European friends), and that it has a reading you’ll understand (°C or °F).

All this said, I can report that this system has been bulletproof for me just about five years now, in multiple different setups, including with inline heaters. The only time I’ve had to ditch a heater was when the glass cracked and was taking on water, Captain.

So really, in short, this is an alternative option to trusting the internal calibration and thermometer sensitivity of standard aquarium heaters. My fish have thanked me for not broiling them, yours can thank you as well.

Disclaimer: If you’re not knowledgeable with electricity and wiring please do not attempt to DIY this hardwired version. Be smart and make good choices. I’m not responsible if you exceed your limitations!

Where to buy (NOTE: these are available all over the place, and in lots of different brands, I’m just linking to Amazon as an example):
Controller (no outlet): Inkbird All Purpose Temperature Controller
Female Plug Connector (for hardwire option): Grounding 3-Prong Cord Outlet
Power Cord from Controller to wall: General Use Appliance Extension Cord
Controller (with outlet and power cord): Digital Temperature Controller With Outlet