Tank heat issues, can I run no A/C vents?

[geaux xman]

I work nights and the A/C was off last night. Came home and my 180g FOWLR was sitting at 82-83 degrees. I also just realized that the A/C vent had been closed all this time. Maybe I closed it during the winter and forgot about it.

But anycase, even on good days my tank has been around 80 degrees. Now that I've taken the A/C vent off, theres a whole lot of cold air blowing almost entirely directly over the tank. The vent obstructs a lot of air. My small QT tank in the bedroom sits at 74-75 degrees no problem.

My prefer temp is around 74-76 degrees. So can I keep the vent off?

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[James77]

You can, the vent only really directs air, the main intake is where the filters are.

82-83 is not a horrible temp to be at, nowhere near dangerous if the tank is used to fluctuations. On summer days with the AC off mine runs 84-86 and everything could not be happier. The only time heat really poses a problem is when it spikes and the animals are not used to it.

[geaux xman]

Thanks for the feedback.

I know theres no real harm at exposure to low 80s short-term. I just think these fish, tangs especially would be calmer and have a lower metabolism running the tank at lower temps. I think I've read before that some of these Australian angels natural waters are slightly colder too. Same with where the achilles reside, sub-tropical.

[dzfish17]

My tank stays around 80-81 in the summer... I dont see a problem.

[uncleof6]

Thanks for the feedback.

I know theres no real harm at exposure to low 80s short-term. I just think these fish, tangs especially would be calmer and have a lower metabolism running the tank at lower temps. I think I've read before that some of these Australian angels natural waters are slightly colder too. Same with where the achilles reside, sub-tropical.

You have perhaps by accident, or perhaps by intent, touched upon a topic that is most often dismissed very causally by the vast majority of reef keepers. It applies pretty much across the board to all our critters, save perhaps those from areas subject to extremes, such as intertidal zones. This topic not only includes metabolic rates, but dissolved oxygen levels as well. What it comes down to, (without setting out to bust the mythinformation concerning gas exchange and a few other subjects) is higher temps increase metabolism, and this applies to all biological activity in the tank (bacteria included.) Increased metabolism increases the Biological Oxygen Demand (BOD.) Higher temperatures decreases the oxygen saturation level. Meaning that less oxygen is available being used at a faster rate.

Saturation (at sea level) for salt water @ 75deg;F is 6.9ppm (at higher elevation it will be less.) 80% of saturation level is considered "safe," in this case 5.52ppm. It is difficult (but very doable) to maintain saturation levels, however the 80% is not so difficult to achieve. Problems with oxygen level begin at 4ppm, and fatalities are possible not much below that, with definite fatalities @ 2ppm.

Raising the temp to 86° as mentioned above, brings the level down to 6.2 at saturation and 80% would be 4.96ppm, lowering the margin of safety considerably. At 2000' above sea level, or in a tank that has a high BOD, (high bio load/poor maintenance/poor gas exchange) this could be potentially dangerous. Adding a heterotrophic bacteria culture, and the subsequent bloom, could easily kill the tank off--(hint hint) by depleting the oxygen to fatal levels--though this is possible in any system.

It is well established that higher oxygen levels promote fish health (less disease prone) and growth rate is better. Lower temperatures allow higher oxygen levels--a wider safety margin. Many problems in marine systems can be traced to low oxygen levels--if you trace the problem past the pat answers usually given.

The only way to know if a particular temperature is creating a problem in your tank, is to know the oxygen level, and the only way to know that level is to test for it; for reasons that defy logic, testing for this is overlooked or discouraged. It happens to be more important than the nitrate level. What will be a problem is system dependent, i.e. it will vary from system to system. So 86 might be fine in this system, but will cause some serious issues in another system.

[geaux xman]

uncle06,

Did you look at my numbers wrong? I'm interested in keeping my DT below 76. I agree with the better oxygen content with lower temps. I've tried the fan in the sump, that dropped the tank about 1 degree. I'm not interested in a chiller yet. I'll monitor the next couple of days to see if I get good temp improvements with the A/C like that.

[uncleof6]

uncle06,

Did you look at my numbers wrong? I'm interested in keeping my DT below 76. I agree with the better oxygen content with lower temps. I've tried the fan in the sump, that dropped the tank about 1 degree. I'm not interested in a chiller yet. I'll monitor the next couple of days to see if I get good temp improvements with the A/C like that.

I was driving home the point you touched on--in other words I am agreeing with you. Went off on a rant on why this is an important topic that is pushed aside and dismissed casually by the majority of the hobbyists.

I don't see any problem with the vent being open, and if you can get by without a chiller that is a good thing. Keeping temps lower is not an inexpensive pursuit, which is why it is pushed aside and dismissed as not being that important.