Which thermometer is correct.

[PhreeByrd]

@ca1ore is so right. Affordable thermometers are always going to have some inaccuracies, and if you can find specifications on them, they will list the tested accuracy. It's almost never better than +/- 1 degree F even for the best of them. The cheaper ones cannot be expected to be better than +/- 2 degrees or so. The temperature display on my old Reefkeeper 2's is the best I have found, and even it has an specification of +/- 0.2 F, IIRC.

All that said, I remain convinced that stability and repeatability are far more important than the actual number.

 

[Snoopy 67]

https://www.amazon.com/Tropic-Marin-ATM50002-Precision-Thermometer/dp/B00025YUT0

This should fit the budget.

 

[Kenneth Hooper]

A degree isn't going to kill your fish. It really shouldn't matter much at all if your tank is 78 degrees F but reads 80F or vice versa. What matters most is that the temperature remain as constant as possible.
Either of your 'inaccurate' thermometers will work fine in keeping your temperature constant and within the range of 78F - 82F

 

[drblakjak55]

Funny. I found digital at 78.6. One floating alcohol type with bearings at bottom at 77.7. Old Combo alcohol/hygrometer at 76.8. Stick on at 76. But I set my Finnex Heater at indicated 83 to get those results. Haha

 

[drblakjak55]

Funny. I found digital at 78.6. One floating alcohol type with bearings at bottom at 77.7. Old Combo alcohol/hygrometer at 76.8. Stick on at 76. But I set my Finnex Heater at indicated 83 to get those results. Haha

 

[Snoopy 67]

My floating alcohol with bearings matches my tropic marin pro.

 

[Gene Ashton]

I disagree. Temp being rock solid is one of the most important parameters. If your temp is changing it’s also changing your available oxygen, which changes pH, which effects corals ability to calcify, numerous other negative effects as well. Stability is key is reefs, having stable temp helps keep everything else in line and not fluctuating.

I went from running my 90 with heaters with internal temp control, thought my coral was doing well. I was wrong, after upgrading my heating to a ranco temp controller and titanium heaters without internal temp control, my coral took off, much better pe, more growth. My whole reef is much more stable in general (minus the power outage I had last week). My temp doesn’t fluctuate at all now. 78 rock solid 24/7. Where as before I went up or down 2 degrees around 78. So I’d say it definitely matters and have first hand proof in the pudding.

Ive been trying for stability. What do you think about the new BRS controllers and BRS Titanium heaters? I'm thinking about using the BRS controller and two Titanium 200W in my 115 gallon RSR 450. I currently run about 77.5 all day long

 

[Hemmdog]

Ive been trying for stability. What do you think about the new BRS controllers and BRS Titanium heaters? I'm thinking about using the BRS controller and two Titanium 200W in my 115 gallon RSR 450. I currently run about 77.5 all day long

I haven’t tried them. I would still pick a ranco over anything. The heaters are probably fine.