Marina Floating Thermometer with Suction Cup

It's cheap, it works, and it stays put. Not sure how much else you need to know. This is a thermometer for a fish tank, not a superconductor.

Every aquarium needs a thermometer, and in my opinion, this is the best one to have. You never have to replace batteries like the digital kind, it's more accurate and more attractive than the black stick-on kind, and it doesn't interfere with the lid like the metal hanging kind. My only complaints are that there is a fairly narrow viewing angle on the mercury (red line), and the clear suction cup that it comes with can turn white and lose its flexibility after a while. Otherwise though, it's a great little thermometer and I recommend it over any other.

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This is now the third thermometer I've had on my current fish tank. It's also the best one.

The readings on one of these thermometers is generally more accurate than that of the adhesive strip you can apply to the front of the tank. The suction cup is also good on this one--I had to get rid of another one because of that problem.

You'll need this no matter what kind of fish tank you have so you can adjust your heater.

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As a thermometer, it seems to work fine.

But if you're using it in a acrylic tank, DON'T USE THE SUCTION CUP! It left two permanent ring shaped marks on my tank, after about a month of use. I can't get them off by scrubbing or rubbing, or even scratching with my fingernails. (added a picture of the mark to the product images)

Be warned!

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This works perfectly with my aquarium, exact temperature is displayed and also a convenient "green zone" marked to know the temperature for tropical fish.