Many aquarium hobbyists and folks in the aquarium trade look for ideal conditions for their marine animals. Temperature is often debated and people swear by one range or another with much conviction. In this article, we will take a practical approach and discuss the ideal temperature for saltwater aquariums. It is worth mentioning that some people keep cold water fish species such as those living off the coast of Southern California, but for the purpose of this article, we will discuss the majority of saltwater aquariums which consist of warm water marine species typically found in the Tropics, the Red Sea, The Great Barrier Reef, etc..

Why is temperature important?

Temperature in saltwater fish tanks is the parameter that is most often attributed to aquarium failures and “tank crashes.” Fish and other marine creatures have a difficult time processing oxygen and functioning overall at temperatures that are not ideal – this will lead to sick animals or worse dead ones. This is why temperature is so important to understand in order to have a successful aquarium.

Temperature Stability

We will discuss the temperature range in the next section. First, it is crucial to understand that temperature stability and the prevention of a big temperature swing is as important as the temperature range. I recall losing a few fish when my aquarium had a 5 degree swing in a single day – all within an acceptable range of temperature. The fish we keep come from stable water conditions where swings may occur over a long period of time – for the most part, the fish are used to stability – that is the key to success, not just for temperature but for all things aquaria. I would recommend a maximum of 2 degree temperature swing in a 24 hour period. Your aquarium may have a bigger swing throughout the cold and hot seasons that occur over weeks and months – and that is normal and acceptable within the safe range.

Temperature Range

Let’s start by looking at temperatures in the Ocean’s Reefs where our aquarium inhabitants come from. On the low end, water temperatures drop to 75 degrees Fahrenheit with some exceptions in the red sea and other reefs where water temperatures may drop lower. On the high end, 86 degrees Fahrenheit is the maximum with some more extreme temperatures in certain areas for a short duration. In saltwater aquariums, we want to keep a small temperature range that will be more encompassing of species from both ends of the spectrum and thus 76-82 is what I consider “safe”. We tend to keep our aquariums across the board at 78-80 because it allows for a 2 degree safety net in case of a problem. Also, it is worth noting that in my experience the fish and other marine animals can cope with lower temperatures much better than higher temperatures. We’ve had a few cases where clients’ tanks got down to 72 degrees with no harm done. However, we’ve lost fish and had ich breakouts at 83-84 degrees.


I hope that everything we’ve covered in this article makes sense to you and helps with your saltwater aquarium. To reiterate, keep the water temperature as stable as possible and keep it in the safe range we discussed and I promise you that you will have much success with your fish, corals and other marine invertebrates.