Temp difference between sump and DT?

[cmor1701d]

I would expect about a 1 degree difference between the sump where the heaters are located and the display tank. I'm seeing a 2-2.5 degree difference. Not terrible but I'm wondering if it might be because the return pump is only able to run at 50% or so.
Tank is 210 gallons, sump is a ~40 gallon Trigger systems CR44.
I have a Finex 800w titanium heater in the first section and a 300w heater in the refugium section. Both are on Inkbird controllers. The 300w is my backup and set 1 degree below the 800.
The return pump is a Current -USA eFlux DC 3170 gph pump. They are sending me a new controller to replace the original which causes the pump to start/stop when trying to run it over ~50%. I guess I'll know for sure next week but wondering if others are seeing a 2 degree or more difference between the sump and DT.

As an aside, when I left the hobby 10 years ago the general rule was running a reef tank at 80-82 degrees as that's what the Pacific reefs we're at. Now I'm seeing the recommendation for 75-78 for most SPS coral. What changed?

 

[EeyoreIsMySpiritAnimal]

Both are on Inkbird controllers.

Where are the temperature probes located?

 

[killer2001]

As an aside, when I left the hobby 10 years ago the general rule was running a reef tank at 80-82 degrees as that's what the Pacific reefs we're at. Now I'm seeing the recommendation for 75-78 for most SPS coral. What changed?

I think the general consensus is 78-82 degrees but more favorable at the lower end in the event temperature rises you have a little buffer zone to work with. If you keep your tank at 80 or 82 you might not catch a temperature spike in time before its too late and death occurs.

 

[TheBear78]

Are you measuring the sump and DT with the same thermometer?
Where are your probes located for each inkbird?
Are both Inkbirds calibrated/synchronised?
I'm wondering if you're simply seeing a tolerance variation between different components.

 

[FSP]

Good calls on the probes. I also wonder what the difference between the room and tank is. 800w could easily be underpowered for a setup like that.

 

[EeyoreIsMySpiritAnimal]

Good calls on the probes. I also wonder what the difference between the room and tank is. 800w could easily be underpowered for a setup like that.

I'm not sure what kind of indoor temperature would be needed to render an 800w heater ineffective in a tank around 200 gallons... I keep a 100 gallon system at 78f with indoor temp of 70f and have a 150w heater

 

[cmor1701d]

All the probes are in the sump. Testing is done with a Hanna temperature probe or a scientific glass thermometer. So I test in sump where the heaters are and in the display tank using the handheld Hanna probe. Both Inkbirds are within .1 degrees of each other.

The reason for also having a glass thermometer is that I used to see a 2 degree difference between glass or cheap plastic mercury thermometers and digital probes. I worked in pharma at the time and asked our quality metrics folks to check both for me. Precise temperature control is rather important when making drugs. They saw the same 2 degree difference and said the mercury thermometers were correct. Their very expensive electronic thermometers are calibrated against the type of glass thermometer I have. I was concerned because at 80-82 degrees, being off by 2 degrees could be catastrophic.
Things have improved as the glass thermometer reads within .1 of all the electronic probes.
I'm now setting my tank for 78 high with a low alarm at 76.

Thanks all for the replies.

Oh, btw, as the tank is directly in front of the house thermostat, I replaced that with an Ecobee and 2 smart remotes. The main unit still controls the HVAC, but the main unit is not used to determine room temperature. The 2 remotes do that. Gotta love the new tech.

 

[Uncle99]

I doubt the two temp measuring devices are accurate enough to measure that small difference.

 

[TheBear78]

Is the DT temp higher or lower than the sump? I couldn't decide...
You've obviously covered all the bases in terms of equipment!

 

[cmor1701d]

Are you referring to a .1 difference? I agree. It doesn't matter when they're that close. Two degrees is a different outcome though.

 

[cmor1701d]

The DT is lower than the sump. I'm hoping that when I can crank up the return pump the difference will narrow.

 

[TokenReefer]

In which direction is the difference (sorry if it was in here but I didn't see it..)? Is the DT lower or higher than the sump?

 

[TokenReefer]

If you pour hot water into a larger container of cooler water you're going to lose some heat... no?

 

[TheBear78]

Have you checked the temp all around the DT? If it's consistent in the DT but simply higher in the heater chamber I wouldn't be too concerned.

 

[EeyoreIsMySpiritAnimal]

Has this been going on for a while or just since the weather has gotten colder?
If you're losing that much heat from the display, you might try using glass tops and see if that helps.

 

[Mark Lang]

I finally quit fighting the difference in temperature between my sump and tank. My probes are in the overflow and heaters are in sump. My thinking is two-fold: 1. My fish and coral don't care what the temperature is in the sump. They care about tank temperature. So I measure in the tank (overflow). 2. When I was measuring in sump and tank, trying to chase a solution to narrowing that difference was annoying at best. Now that I don't care what the sump temperature is, I don't have to chase a difference. I check and calibrate probes periodically using a calibrated reference thermometer. Measuring in the larger volume tank gives me more stable results as well.