Most fish found in aquaria are poikilothermic, an esoteric word that simply means that their body temperature is affected by the temperature of the water around them. It also means that water temperature directly affects their metabolic processes. Water that is too cold slows them down and suppresses their immunocompetence. Water that is too warm can become very stressful very quickly and jolt their metabolic processes into overdrive. It follows that water that is too warm or too cold is harmful to animal health and often results in disease outbreaks. Since most aquaria display the dazzling colors of tropical freshwater or saltwater fishes, nearly all life support systems have some type of heater, which can solve a lot of problems or make them, depending on several factors.

Here are a few of the most common types of heaters and the pros and cons of each:

• Hanging heaters – Most hobbyists begin with a hanging glass heater in a back corner of their first tank. A dial on the top of the heater governs the desired setpoint and a small built-in thermostat determines when electricity passes to the coiled wire in the bottom.
  • Pros – These tend to be inexpensive and easily mounted.
  • Cons – These tend to be cheaply made and unreliable. Eventually, water gets inside the glass and starts to wreak havoc on the electrical components. They are also reliant on maintaining a proper water level to work properly. We do not recommend these.
• Submerged heaters – Submerged heaters are generally mounted on suction cups in the lower half of an aquarium. Output is controlled by a small knob on the top and a sensor somewhere in the body or governed by a built-in temperature control that must be kept dry.
  • Pros – Depending on the manufacturer, these tend to be better made and can be more reliable. They are less reliant on water level and heat more of the water column more efficiently than hanging heaters.
  • Cons – Eventually, even on the good models, water penetrates the heater resulting in malfunction and often, a nasty shock when the keeper becomes a new path to ground while reaching into the tank.
• Inline heaters – These heaters are plumbed inline with other life support components. Water passes through the heating element on its way from the pump to the display. The best titanium models have a flow sensor on the inflow end, which detects when too little water is flowing through and prevents electricity from heating the element and burning up the unit.
  • Pros – These tend to be excellent and very reliable professional-grade LSS components. They are well made with redundant fail-safes to prevent malfunction and loss of life.
  • Cons – Good ones, (and there is no point in buying a cheap one,) are expensive and must be plumbed properly into a life support system for best results.



• In-sump heaters – The good ones are also made of titanium and require a separate temperature controller. If plugged in without the controller, they are always on, which will quickly overheat a system.
  • Pros – These tend to be better made and are very safe and reliable. If the heater is mounted properly where there is a lot of flow, such as near the suction bulkhead fitting in your sump, they can provide years of trouble-free temp control. The controller is typically mounted somewhere dry and has a separate temp sensor, which is best secured somewhere in the display.
  • Cons – Plan on spending at least $100 on the heater, depending on the wattage, and another $125 or more on the controller, depending on whether or not it is controlling a heater or a heater and chiller on the same system. In our opinion, this isn’t really a con, as good heaters and temp controllers end up being very inexpensive and worthwhile insurance against an emergency.

Which heater you choose for your system is largely dependent on the type of system you want, the total volume of your system and your budget. Larger systems require higher-wattage heaters to prevent temperature swings due to seasonal changes, drafts, ambient room temps and other factors. If you would like to consult with a professional PDX aquarium service provider to find the right heater for your system or you would like us to install one on an existing system, just give us a call at 503.784.4403 to schedule a consultation. This is one of many aquarium consulting services we provide for our clients and when it comes to heating your system, it’s definitely a good idea to consult a pro if you have any questions at all.