Temperatures for Corals


Reefing newb
Since setting it up I kept my tank at a very stable 77.5 degrees. I never actually saw it change and I verified the temperature a couple times a week with a digital meat thermometer (outside of the tank obv.).

The other day my girlfriend and I decided to shut the AC off for the year as the external temperature had fallen and isn't expected to rise above 75 degrees again this year (unless there's a fluke). I cam home on the first day and the ambient temperature in the room where the tank is was about 79 degrees. Curious, I looked at the tank's temperature....82 degrees! I was a little surprised and a little worried. I turned the lights off early and let it sit but it stayed there, so I opened a window and it came down a little bit. I know that temp is no big deal but that's a big swing I'd rather avoid.

The thing is, though, none of the corals had ever looked better. Everything was open even more than normal....ESPECIALLY my ricordea mushroom...which almost doubled in size compared to normal. They seemed to be loving the warmer water.

Most of the stuff I read and continue to read doesn't recommend stable temps. this high...and its strange that the corals like it considering most of my corals and fish are from the Indo-Pacific where the temps are more like stable high 70's...which is what I was trying to replicate.

I believe I'm going to try and keep the temp at about 80 from now on and see how it goes. The only thing that worries me is oxygen levels and having that extra buffer if there is an equipment malfunction or power outage (although I feel the outage is more likely and having a slightly higher temp with winter coming will be a good thing I suppose).

What are your experiences with corals and water temperature?
80 is fine. My tanks have always stayed at 82 to 84. That's on the high end of where it should be, but without a chiller, I had a hard time getting it any lower. You shouldn't have any issues with it at 80.
Yeah I know.

I'm more wondering what other people's experiences have been at different temperatures?

Did you ever keep your tanks at another temperature and observe differences in corals?
Temperature stability is not a big deal with my system. Its located in a walkout basement so I'm sure that has something to do with it. The AC nor Heater rarely ever run on this level of the house. 110* or 9* outside it stays pretty stable in here.

I started out running at a stable 78. This was FOWLR and everything seemed fine. Over time I pushed up the temp. Added corals and the tank matured. I will say that at around 81* my corals seem to look better. However, I got a lot of algae growth at that temp. I have since lowered it back to 79.5. My corals look okay, but not as big as they have in the past. Mushrooms specifically. Temp difference or something else? Not sure.

Really its hard for some to grasp that 1 or 2 degrees can have such an effect. I found, with growing Roses, that some like it colder and some warmer. I can't grow a Peace Rose here in North Ga. They just fail to bloom. In N. Illinois I could grow them and they would grow HUGE. During the summer, the temps between the two areas only vary slightly. (Yes, its get hot and humid in Chicago too!) Yet the plant will not grow properly with that very slight difference of say 2 - 4 degrees. I'm sure a slightly more advanced life-form, like corals, can have major differences with slight temperature variations. The trick is to find that sweet spot.
Even if ambient temp is cold it will take a long time for the water temp to fall but the lights will raise the temp up high fast.
I once put a 5G bucket with 80 degree water out on my porch in freezing temps, came back 20 mins later and it had hardly dropped a half degree. With the lid off the temp dropped only slightly faster.

If your light raises the temp up to 80 and then overnight it drops down to 77 your corals will suffer! 80 is fine but it is the temp swings that will kill your corals.
I'm sure a slightly more advanced life-form, like corals, can have major differences with slight temperature variations. The trick is to find that sweet spot.

This is correct. This is why just a couple degree difference in ocean water temperatures has the potential to wipe out reefs.
I'm not sure that the point of this topic really got through, but thanks for the replies anyway guys.

This wasn't really a request for help. There's really no help needed. My tank temperature is stable. For four months it was a constant 77.5 degrees and never wavered even a little bit from that. I have LEDs so they don't heat the water really.

Recently, though, the ambient temperature in the room rose from 72 degress to 79 degrees and I did not have the AC running anymore or the windows open...so the tank teperature DID rise to 82 degrees.

If anything, everything looked BETTER....which encouraged me to reset my situation and am now keeping the temperature at a constant 80 degrees instead.

I noticed a stark difference in my corals when I warmed the water by just a few degrees.....and it was a GOOD difference. Which is now continuing to contribute to the tank looking better than ever.

So there's no problem. I just thought I might ask if anyone else had had experience at multiple different temperatures and seen differences in their corals at different temperatures. I wasn't really asking what you keep your tanks at as I know almost everyone keeps them in the 77-81 range.

It was an unintentional experiment that worked out really well and it had unexpected results I thought I'd share.
My tiny tank saw a bit of temperature swings over the summer (it's much more stable now that the ambient temp is more stable).

81 seems optimal for me.
Do you have a wide variety of corals from different locations? Mine seems about the same but most of my stuff is indo-pacific...which I would have thought would like the sub 79 temps.

I just find it a little weird but it's always nice to see things even more open. Means I'm doing something right :)
My tank is mostly softies (a wide variety of zoas) since they're a little more forgiving of the swings that I'm sure happen in my tank.

I do have a couple LPS', but nothing aside from that.
This thread may of saved my coral (maybe..I dauh know)

I'm new to corals and reef tanks.. but an old salt with fresh water aquariums... so I hadn't been concerned (enough apparently) when my tank was dipping to 77 / 78° at night and to as high as 82° by day. I can't afford the chiller I need yet on my hobby budget so I was winging it. SO now, I've wired in the STC 1000 I had purchased and have it set to 27.4C +/- .5 (Which I calc to a diff of .9°f) this should hold my temp at between 81 and 82.. but now I'm worried that tomorrow after being 80 all night it may go even higher.. I may be breaking out an ice cooler of ice and a long coil of poly tube as an emergency chiller tomorrow evening.. hummm this is scarry.
Get a clip on fan to blow across the top of the tank. The added air movement will increase evaporation and this will help keep the tank cool. Most tanks do not require a chiller. There are members on this site who live in very hot climates and just run fans.
Thanx..!!!! all help grabbed up with a hug..

I have a 40" 5 blade ceiling fan buzzing away right over it.. But I have two 100 watt MH lamps in my light assortment... love the light frequencies beaming down like the sun but hate the heat. I have a clip-on on my sump at the spillway into the last chamber.. I had it off today.. that sucker is going back on!

Good point and I have a RODI ATO so evap is no problem..... and I have another clip-on fan somewhere... humm.. need to dig that sucker out.
Last edited:
Get a clip on fan to blow across the top of the tank. The added air movement will increase evaporation and this will help keep the tank cool. Most tanks do not require a chiller. There are members on this site who live in very hot climates and just run fans.

OK... good stuff.. thank you... these days with forums full of experienced brothers and sisters in the hobby... wow, what an asset!!!

This afternoon I will wire fans to come on as a chiller.... you guys are great. Being a retired machine design engineer I should back up and kick myself for not getting that day-one.

--- Keep It Simple Stupid! ---

T H A N K - Y O U !!
Last edited:
If you can wire the fans to kick on at a certain temp, that'd be cool. I always plugged mine into the same timer that the lights were on, so that they'd automatically run whenever the lights did.
Geeze typed all this up and it vanished...

OK, I did wire the fan and heater to my STC-1000 (these things are about $35 give or take a couple to your door). I say fan because the two little ones I had rigged last night per your advice did the trick, but not quite perfectly. They DID keep my tank to 78.8°f today. That is a HUGE difference. So I put a larger more efficient fan on the light bar and it had already started to bring the temp down some in about an hour.

You guys and gals ROCK!. Living Reefs ROCKS!

So..I have my fans coming on at 77.56° and going off at 77°. My heater will kick on at 76.44° and off at 77°. (remember this is a $35 item that is doing this)… So if you want to know more and need advice to wire one in.. just shout. You can get them lots of places on-line. BUT... watch for one that is shipping from inside the states if you are in America. ... They are also easy to get in Europe.

I’m a retired machine design engineer and will share what I know with my reef friends .... BECAUSE ....I sure need some shared experience at this reefing hobby.

Next will all this blahh blahh really do what I hope it will?? ……. stay tuned.

OK, my copy of Borneman's "Aquarium Corals" came today so I have some serious studying to do.. ..

again... THANX to all those that help this "don't know squat about reef tanks" guy.
Last edited: