Several suitable heating methods are available to the hobbyist:

1)  the combined heater/ thermostat
2)  the glass tube immersion heater controlled by an external thermostat
3)  under - tank heater mat controlled by external thermostat.

  Of these, the combined heater/ thermostat remains by for the most popular choice.
 Glass tube immersion heaters have declined in popularity over recent years, even so it remains a good choice.
  Large tanks, in particular benefit from having several heater units in different locations, all controlled by on accurate thermostat. This method generates efficient heat dispersal and maintains stable water temperatures.
  The optimum temperature for a tropical marine aquarium is 25o (77oF). Livestock will start to suffer below 22oC (72oF) and above 27oC (80oF).

CHILLING

  This occurs when the temperature rises dangerously out of control. Any aquarium with high intensity lighting may overheat, especially if the room temperature is also high.
  Tropical, and even temperate, climates may experience pro longed day time temperatures well in excess of those recommended for the aquarium simply turning down the heater- thermostat will not reduce the temperature of the tank below the temperature of the room.
  To keep room temperatures down, hobbyists can keep blinds or curtains closed to reduce the amount of sun on the tank. Also, a tank containing light invertebrates can have their photoperiod reduced.