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    It is essential to maintain a stable temperature, and more importantly avoid rapid changes, in order to avoid stressing fish, coral and filter bacteria. Temperature along with pH is part of the reason why soaking the bag that the fish is in on the water’s surface is so important when being introduced.  

    Temperature in an aquarium should always be kept constant and depending on the species the following temperatures should attempt to be kept as ideals through the year.

    Fish type

    Degrees C

    Degrees F

    Tropical Marine fish and coral

    24 to 25

    75 to 77

    Mixed Tropical fish

    24 to 25

    75 to 77

    Cichlids tank

    24 to 25

    75 to 77

    Discus tank

    26 to 28

    79 to 82

    Native marine tank UK

    6 to 10

    43 to 50

    Coldwater fish tank unheated

    10 to 24

    50 to 75

    Koi Pond heated

    16 to 26

    61 to 79

    Outdoor Pond unheated

    5 to 30

    61 to 86

    A seneye device can be used to set up temperature monitoring with alerts.

    Temperature problems are one of the most common issues that aquarists face, here is some advice on correcting heaters. 

    Common causes of temperature going up are; a failed heater that is stuck on, ambient temperature rising, a failed chiller or the temperature is not set correctly on a thermostat.

    Increased temperatures bring a decrease in the oxygen-carrying capacity of the water. As oxygen levels fall beneficial bacteria levels and fish can become starved of life giving oxygen. The fish will often appear to gasp at the surface if oxygen levels drop. However, this gasping can also be symptomatic of high NH3 levels.

    Take steps to lower temperature gradually.

    Decreased temperatures slow the fishes' metabolism down, in tropical fish it can slow down to a life threatening and even fatal rate.

    Common causes of temperature going down are; heaters not being plugged back in and heaters not being powerful enough to overcome the heat losses.

    Take steps to raise temperature gradually. Only make small adgustments to heaters to raise temperature if they are not constantly on. If you make a small adjustment wait a good few hours before making another one. If the aquarium heater is constantly on it may be broken or not producing enough heat for the size of aquarium.

    Tip: always unplug heaters before placing hands in water and always use a drip loop on the cable to prevent water entering plug sockets.