How stable must water temperature be?

I am a newbie, so pardon me if this is common knowledge. I have been doing a lot of reading on keeping a mixed reef tank. One of the themes that comes is water temperature needing to be "stable". My problem is I have a 140 gallon bow front tank that is only 18" deep (72 wide and 30" tall). I have a Apex controller that is telling me my temp takes a 2 - 3 degree swing during the day (81.1 - 83.1). I have cut back my LED to 90% with no big effect. I don't have room for a chiller in the cabinet, or elsewhere.



Is this going to be a problem?

 

IMO 2-3 degrees should not be a big issue, swings of 5 and above are of concern.

i have an open top tank and my temp if static at 26°c

 

That's not a big shift. You see daily fluctuations in the ocean too. My tank fluctuates from 77-80 degrees.

What is your house temperature and where do you have your heater set too?

 

During analysis of the temp I unpugged the heater. I wanted to make sure the heater was not tuning on at the wrong temp. It was set at 81. Now that I know I can let it swing I will set the heater at 82. With a lights cut off at 85.

The house A/C is set at 72.

 

no you're okay man. My heater is set to keep the water at 79, and during the day at the hottest point my tank hits 84 or 85, pretty big swing. it's a small 10 gallon, so that might have alot to do with it. But i'm guessing my fish and coral are used to it, as there seem to be no ill effects

 

Well if you turn the heater down a tad, you won't have to worry about the high end swing. I would set it around 78 and let the light bring it up to 81 during the day.

 

Agreed (with running it around 78). No reason to go any higher.

 

2-3 degrees is perfectly normal though always above 81º is high to me. IMO the ideal temperature is 78º,+/-2º. If you want to keep your temperature down there are a few cheaper options than a chiller:

1. Can you put an A/C in the room? Cooling and drying the air will cool the tank down a lot. Edit: didn't see you have a A/C.

2. Evaporation is key for cooling a tank. If you can run a fan near or across the surface of the tank water you'll increase evaporation and cool off the tank. I use a vornado air ciruculation fan pointed toward the ceiling near my tank and that drops a degree off the tank temp usually.

 

Is your heater controling itself, or do you have it turned all the way up and the Apex is turning it off and on?

You want the latter... sorry if I'm telling you stuff you know. Ya, I agree with others, set the heater to go off sooner if it is even coming on at all so the tank won't swing to 83. But a 2-3 degree rise itself is not a problem.