How much is too much temperature swing?

[jaymer]

My tank goes from 77.8 to 78.6 throughout the day. Is that too much of a swing?

 

[tbrown]

Not really. Some tanks go 4° up and down during the day. Mine usually goes about 2° up and down on the small tank and about 1.5° on the big tank.

 

[exnisstech]

If I'm running on heaters I set them for a 1 degree swing for no particular reason. When it gets hot outside I've had as much as 5-6 degrees swings with no noticeable I'll effects.

 

[Quietman]

In nature reef temps can change several degrees throughout a day and seasonally average temps can vary 5-6 degrees.

 

[KrisReef]

My tank goes from 77.8 to 78.6 throughout the day. Is that too much of a swing?

No. It's not like any of your fish are going to rush under the rocks looking for a sweater when it hits 77.8

Less than a degree is very stable for corals and fishes!

 

[winxp_man]

My tank goes from 77.8 to 78.6 throughout the day. Is that too much of a swing?

Simple answer no. But not all tanks are the same. And if you can get stability it’s what you should stride to achieve. Temp being part of the stability equation.

 

[BriDroid]

I keep mine as stable as possible though I’m not sure it’s needed. My tank temp moves between 75.2 and 75.7. My sump (where the heaters are goes between 75.3 and 75.9. I’m using 2 Eheim 100W heaters and a clip on fan over my sump all controlled via my Hydros.

 

[Tangdora]

I’m in the 2 degrees max bucket.

 

[ISpeakForTheSeas]

Just to add to this - as mentioned, some swing is just fine; what your corals are used to can impact how big of a temperature swing is too big, but there are some general guidelines and thresholds that may be helpful:

Slightly diurnally and seasonally, yes:
"The diurnal temperature variations are about 0.3°C in theopen oceans and 2 to 3°C in shallow waters."
Source: https://www.academia.edu/36838790/Chemical_Oceanography
From what I've seen, for most tropical reef organisms, as long as the temp doesn't swing too far too fast, and as long as the temp is kept within ~75-82F (lower than 74ish can start causing problems, higher than 83 and many corals will start to bleach - so allowing for temp variation due to imperfect temp controllers in our tanks, I would set 75F as the min and 82F as the max), the temp doesn't seem to matter much. To give an idea, a 2C change (from 25C to 27C, for example) is about a 3.5F change (77 to 80.6, with the 25C to 27C example), so allowing a 3F to 4F temp change diurnally should be fine.

I’ve been reading through a bit of literature on corals and temperatures, and - generally speaking - 83F is considered the safe limit you don’t want to go beyond, so some people might recommend not going above 82 as a precaution.
Edit: when accounting for the slight inaccuracies of our heaters/controllers, I personally would set 82F as the limit.

That said, though, there are a number of caveats that determine what temperature is too high. To list a few:
1) the location the coral was collected from (some coral reefs have higher temperature tolerances based on their geography than others - 83F [technically like 83.6F or so] is the limit for the least heat resistant reefs, if I recall correctly; I believe somewhere around 87-89F was the limit for the most heat resistant).
2 ) temperature stability (the more stable the temperature the coral is used to, the less it’ll like changes to temperature).
3) how long the coral has to acclimate to the higher temperature (slow and steady wins the race).
4) corals can handle temperatures above their temperature limit for a limited amount of time (if the temperature is only slightly over, the corals only start showing distress/begin bleaching after a few days [four days at 1-2F over, if I recall correctly]; if the temperature is significantly above the limit, the corals will show distress/bleaching within hours).

So, as Tamberav and a few others I’ve seen here on the forums can attest, 86 may not be too hot, but - personally- if you’re going to run a tank that hot I’d take things nice and slow (likely ramping up over the course of a month or two) to get the corals there as a precaution.