How much daily temperature fluctuation is too much?

[Ryan S]

I found an article that says the ideal temperature range for reef aquariums is 76-83 degrees. Randy Holmes keeps his tank at 80-81 year-round. He also said that many of our fish and corals from reef areas that are 83-86F in the wild, but because our systems are closed, that's why the lower range of 76-83. He doesn't mention fluctuation however. (76-83 is not a fluctuation allowance, but the ideal constant temperature for a reef tank).

 

I read on another forum that a guy kept losing fish. He had a 3 or 4 degree daily fluctuation, so he added a chiller, which kept the fluctuation at 1 degree, and he stopped losing fish, and has added many since that are perfectly healthy. Could the chiller (and lack of temp fluctuation) be the reason for his success?

 

I always thought some fluctuation was fine, and might actually make the fish and corals hardier, but maybe that's a reef myth?

[smallreef]

The problem with fluctuation is ours is SO rapid... on the reef it takes 2-6 days for a 3 degree fluctuation... in our tank it happens in hours...

 

I TRY to keep it to 2 degrees within a 24 hour period.. though its not always that easy... I have had sever fluctuation (not in this tank but in a 150g FOWLR) and didnt have any noticeable repercussions...

[Fishie]

My temp doesn't not swing more than 0.6 usually in a 24 hour period

 

I also usually set the overall temp to around 81 in summer and 79 in winter

[Chad]

There are many places on the reef where temperature can swing rapidly... current may change and cause local temperature to change 5 degrees in a couple of seconds...

 

You'll hear stories from time to time of something similar happening in someone's tank and everything from bleaching to RTN ocurring.

 

What's the difference? Honestly, I'm not sure we know for sure...

 

But here is my thought. I think it's the consistency of it all. If your tank changes every day from 78-84 and then back over the course of the night. That's acceptable, I've seen lots of people with temps that follow that pattern with nice looking tanks. However, if your temperature normally changes from 80-81 over the course of the day, and then one day a heater stays on that shouldn't and you go from 81-87, that will likely cause stress that may kill some corals.

 

My advice? Fine something that works for your tank and try to make it as consistent as possible. Watch your temp fluctuations over the course of the day and (instead of fighting what it does) guide it to something consistent. Whether that's a 1 degree fluctuation or a 6 degree fluctuation, go for the same thing every day.

 

(FWIW, mine is usually 79-81, but sometimes dips to 78 or rises to 82 which seems to be mostly weather dependent)