Thermometer - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 22 Old 05-25-2009, 01:16 AM Thread Starter
Arrow Thermometer

What thermometers have you guys had good experiences with? ANybody tested to see how accurate they are? I have two of the regular glass type that stick to the glass. They are about 10 degrees away from each other when they are in the same tank. I'm looking to upgrade to something much more reliable.
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post #2 of 22 Old 05-26-2009, 12:57 AM Thread Starter
..nobody knows what thermometers work well?

I should add that the ones i have now are the floating glass type that have the suction cup rather than the type that stick to the outside of the tank (we all know how inaccurate those are).
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post #3 of 22 Old 05-26-2009, 08:05 AM
Fishin Pole's Avatar
i bought a whole lot of thermometers all at once and tested them in one tank and they were all within a degree of one another......I have seven tanks right now and wanted to make sure all were giving me the same reading.........As far as a quality thermo i dont really have an answer for that.......I bought whatever was cheap and they all work fine for me.......i prefer the floating type over the suction cup type
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post #4 of 22 Old 05-26-2009, 12:01 PM
I used to use the stick on ones on the outside of the tank and then a suction cup one on the inside and they gave the same reading. I think they're all reliable temperature wise. but some look better made than others in terms of professional look or cheapo look.
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post #5 of 22 Old 05-27-2009, 02:19 PM
Tyyrlym's Avatar
The stick on generally not accurate. If you want an accurate temperature measurement then your instrument needs to be immersed in the liquid. For me the simple glass ones that you stick on with a suction cup work very well. Don't bother with the Coralife digital ones, they're inaccurate and hyper-sensitive.

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post #6 of 22 Old 05-27-2009, 03:42 PM
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I also use the glass ones you can either float or suction cup to the inside. I used to have some Corallife digitals and I found them to be off by about 4-5 degrees F.

I wonder why your glass ones are so far off in the same tank. Did you place them in the same area of the tank to compare or were they at opposite ends? It may be that you heat is not being evenly distributed throughout the tank.

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post #7 of 22 Old 05-27-2009, 04:04 PM
I did not know the stick on ones were unreliable. Ive never had any problems.

For thermometers, I was always told to put it as far from the heater as possible. My old suction cup one broke in my tank once and from then on I haven't used any in-tank thermometers. Anyway, anyone have a brand they can recommend? From the posts here, I'm beginning to think i need to get an in-tank thermometer again.
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post #8 of 22 Old 05-27-2009, 04:28 PM Thread Starter
I too would be interested in brands. I know walmart has them for less than $2, although i would rather get them somewhere else. Petsmart has them for less than $3 i think.

To better answer the questions. Yes, they were side by side in my tank. I was testing them before i put them in the other tank. For some reason they are roughly 10 degrees off. No idea why.
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post #9 of 22 Old 05-27-2009, 10:08 PM
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I use this Zoo Med Digital Thermometer at PETCO

I dont know how accurate it is but it seems to be alright.

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post #10 of 22 Old 05-28-2009, 07:01 AM
Tyyrlym's Avatar
Mine are all Hagen. $2.99 from Fosters & Smith. Due to shipping I always bought them with a lot of other stuff.

The stick on ones are unreliable for the simple reason that they don't measure the actual water temperature. They measure the temperature of the outer surface of the tank material. Well, the people who make the stick ons don't know a lot of factors such as what material your tank is made of, glass or acrylic which have widely varying thermal conductivity. They don't know the thickness of the material of the tank, thicker materials will be cooler on the outer surface. They don't know the temperature of the room you're in, colder rooms make the outer surface cooler. All these factors can impact what that outer surface temperature really is and the manufacturer can't know what they are, so they make assumptions. Maybe they assume it's a glass tank, 1/4" thick, with a room temp of 74 degrees (an example, not the actual assumptions). If you have that kind of tank and room conditions the stick on works great, all their assumption are correct. However the more you deviate from those assumptions the less accurate the reading is.

The only way to reliably measure the temperature of a material is to take a reading from the material itself. I don't trust a thermometer that isn't immersed in the water or a digital that doesn't put it's probe right in the water.

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