Basically, thermometers have two types, some that go inside the tank and other that stick on outside the tank.  The ones that go inside the tank are usually cheaper and can give you problems when you want to see the temperature (unless you don't mind getting your hand wet every time).  The outside thermometers are a little more expensive but are easier to read and are less hassle.

    The choice is up to you as to what type of thermometer you want to buy for you fish tank, but make sure you have one.  Should you decide to go with an external thermometer, make sure that you place it 2 inches above the gravel line.  This will ensure a more accurate reading.

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