The water temperature in your reef tank is one thing that we can easily control. We have heaters
for when our aquarium is too cold, and we have fans and chillers for when our tank’s too hot.
You can even use ice cubes in a ziplock bag in an emergency. But what’s the ideal temperature
for a reef tank packed with colorful fish and coral from a tropical reef,
and why should we even care to stay near it?
Hi guys and girls, I’m ReefMan, and we’re going back to basics and talking reef tank temperature
this week. Most of this video will be about the average warm water tropical reef tank. There are
variations you can use though - deeper water fish and corals prefer cooler temperatures, and very
shallow tide pool creatures can withstand much higher temperatures for a short period of time.
There are even double insulated tanks made for very cold water, but that’s beyond what we’ll
be talking about here. It is very important to know what you’re putting into your tank,
so that you don’t mix animals with different care requirements that you cannot meet.
That Catalina Goby? It wants much colder water than your Clownfish.
So, how low is too low for our usual corals, things like Acropora, Montipora, Zoanthids,
or other large polyp stony corals? What would be a good minimum reef tank temperature?
It turns out, it’s lower than you might think - in fact, branching Acropora can survive
all the way down to about 14 degrees celsius - which is about 57 fahrenheit
for three days before their Zooxanthellae, which contribute so much energy, begins to
leave their tissue - aka they bleach and then die. Surviving is far from thriving through, and
metabolic activity slows and and basically stops around 64 degrees fahrenheit, so while the coral
might survive you shouldn’t expect it to survive long term or to grow at such low temperatures.
Some coral can protect itself against low temperatures by producing a slime coat that
envelopes the coral in a protective layer. Usually massive mounding corals do this, think Favities
and stuff like that, rather than branching corals. You can sometimes see this slime coat in shipping
bags where the coral may have been exposed to less than ideal temperatures during its transport.
Really, there should be no big surprise here. If you do a search online for coral reef temperatures
you’ll find that water temperatures around 73 to 80 degrees fahrenheit are ideal. Most people
target 25 celsius or about 77/78 fahrenheit or so. It’s easy to set a heater so that the
water temperature doesn’t go below this level, but it’s much harder to keep it from increasing
beyond that ideal level. I’ve kept reef tanks as cool as 74 degrees fahrenheit without any issue.
It turns out that average room air temperature might work great,
but lights and equipment contribute heat to our tanks - and of course at night our
lights are not on - so we need heaters to keep the temperature within a stable range.
During the day, temperature will increase - and that’s ok up to a point.
In the south Pacific ocean, for instance, there are reefs that increase in temperature every
day by about 3 degrees fahrenheit and some that approach a 6 degree swing every day.
So it’s fine if your tank swings a degree or two each day. I would caution you against
having a 6 degree swing in your tank, as I feel like that’s an exceptional condition on
these wild reefs, and not something that happens regularly year round.
Think, shallow lagoon or something like that protected from the open ocean water.
The big thing to remember is that you want to avoid holding the temperature at those
elevated levels for a long time. A warm afternoon raising the temperature a degree or two is ok,
a warm sustained summer might kill your corals
in the same way that increases in ocean temperature are killing our wild reefs.
To combat high reef tank temperature, you can use something as simple as a clip on desk fan
that you set on a timer to run in the afternoon when your tank is warmest. A more advanced version
might be to use your tank’s controller to turn on the fans when a certain temperature is reached.
The downside to fans, of course, is that they cool your tank by evaporating water.
This adds a lot of humidity to your home, something that can cause issues.
Another option for cooling your tank, and the one which I use myself, is to buy a
chiller. Aquarium chillers usually work in the same way that your refrigerator does,
and they need similar maintenance over time to replenish their coolant after years of use.
On very small tanks, your chiller may not even use coolant - instead cooling water using a
device called a Peltier plate in a process called thermoelectric cooling. These types of chillers
work best on small aquariums, maybe less than 25 gallons or so in the nano reef range, and can only
drop your tank’s water a few degrees. For keeping even the coldest water species, larger chillers
with refrigerant can keep a tank downright cold. Larger chillers rely on vapor compression and are
also much more energy efficient - but since they have fans and compressors they’re not
silent like a peltier plate based cooler can be. That said, most thermoelectric chillers use
a fan and a heatsink to cool the hot side, and so they’re usually not silent either.
So, why should we care? What’s really going on when coral is under heat induced stress?
When Acropora is subjected to a high water temperature for a long period of time,
it starts to change it’s biological processes to survive. Instead of growing, it produces things
like heat shock proteins which help to repair damage that’s caused by the heat. All this can
only work up to a point though, and all the energy and resources spent on combating heat stress are
resources taken away from immunity, growth, and coloration. In the extreme case, the coral might
even bleach - and then if you haven’t been feeding your coral adequately it’s almost always fatal.
Of course, that’s not ideal in our reef tanks, but this is partially the process that allows
some coral to survive coral reef bleaching events that we see so often in the wild.
I’d recommend setting the average reef tank’s heater to about 77 degrees fahrenheit or
25 celsius. Pick your favorite way of keeping the temperature under control,
and don’t let it go over 79 or 80ish fahrenheit - about 26 celsius.
If you go the route of fans, consider adding an automatic top off system to your tank as well,
so that you don’t cause swings in salinity as you evaporate the water and replenish it all at once.
Don’t underestimate the amount of water a fan blowing over the surface can evaporate!
If you’ve got a nano reef, consider something like the Ice Probe cooler which can reduce an average
10 gallon tank’s water a couple of degrees. You simply need to drill a hole in the tank,
and tighten the device on the glass - a controller turns it on and off
as needed without evaporating all your tank’s water in the process.
Thanks for watching, I hope you found this helpful! Reef tank temperature isn’t too
complicated, but it is very important to get right. Though you can swing a tank’s temperature
5 or 6 degrees every day, I wouldn’t recommend it. I try to keep my tank within a degree or
two over the course of a day, turning on my chiller at 78.5 and off again at 77.5.
Take a moment to subscribe to the channel, and leave a comment with your best tips on managing
reef tank temperature. I’ve included a handful of papers on coral temperature related topics
down below, so if you’re interested in the science behind all this please take a look at
those and dive in! I’ve found paper authors to be incredibly helpful if you have questions for them,
most of them are very excited to talk about their work so
don’t be afraid to reach out to them directly with your questions as well.
Stay safe, be kind to each other, and have a fantastic day - I’ll see you next time.
Bye!