If you can't stand the heat, get out of the...
(Post: About fish tank temperatures)
In a natural setting, if the water is too hot, tropical fish can simply migrate to water that's more to their liking.
But that can't be said when they live in a fish tank.
Water that is too cold makes tropical fish very sluggish and makes it easier for harmful organisms to proliferate.
Warm water, around 80 - 84 degrees F, increases their metabolism; making them more lively and produce fast generations of eggs or fry.
But on the flip side, it decreases their life spans.
Temporary periods of hot water (e.g., above 85 degrees F) can aid in curing stuff like ich. But prolonged exposure to very hot water is fatal.
It lowers the available oxygen and makes oxygen uptake so difficult that fish congregate at the surface, frantically gulping at any aeration bubbles.
I like to keep my guppy tanks between 80 - 84 degrees F. The fish appear more healthy, active. And about every five or six weeks, I see another generation of baby guppies.
Given the importance of water temperature, I've tried many types of fish tank thermometers. As for accuracy and convenience, my favorite is the "stick on label" exterior type, followed by the traditional submersed thermometers.
Last on the list are the battery powered and water probe digital mini-thermometers. Although the display is nice (when they are actually working properly). They're just too finicky, awkward to install, have wide + or - parameters and IMHO, are just plain ugly.
A Note About Accuracy -
Most tank thermometers (worth a damn) have a + or - of one degree C (or 2 degrees F).
You can check its accuracy with the traditional "hot" or "cold" method; that is, measuring its reading to known temperatures like the boiling point or freezing point of water.
Just Google "Checking thermometer accuracy" or a similar search term and you'll find many links to detailed instructions on each method.
Confession: After using both the "hot" and "cold" method several times to check thermometer accuracy , the lazy side of me usually breaks out the digital gourmet cooking thermometer. Lol!
Submitted FYI.
May you and yours be well and loving life today.,
In Lak'ech,
JaiChai