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Aqueon Submersible Aquarium Heaters (300 Watt)

Item: 6104
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Aqueon Submersible Aquarium Heaters are designed for fresh and saltwater aquariums. Each unit is fully submersible, shatter resistant and equipped with an electronic thermostat that provides accurate and reliable heating. Additionally, there is an adjustable heat settings ranging from 68° - 88°, an LED which illuminates when actively heating and a built-in auto shut off function that prevents the heater from overheating. The suction cups make horizontal or vertical installation quick and easy. Available in five sizes to accommodate various aquarium sizes.

Key Benefits

  • Fully submersible with shatterproof and nearly indestructible construction
  • Electronic thermostat with advance gravity shut off technology
  • Adjustable heat settings, accurate to +/- 1° with LED light that illuminates when heating
  • Can be easily installed both vertically or horizontally using the included suction cups
  • For fresh or saltwater aquariums up to 100 gallons
  • Dimensions: 3.5" x 1.5" x 16.25

Useful Information

Aqueon Submersible Aquarium Heaters Instructions

Installation & Set-up Guide


Before working with or installing heater, be sure to read and understand all safety instructions and warnings.

  • Step 1: Attach suction cups: Attach suction cups (D) to heater. Attaching both suction cups will ensure proper positioning in your aquarium and will allow adequate water circulation around the heater for even heat distribution. Suction cups should only be placed over the label portion of the heater as shown in FIG 1.
  • Note: Do not place suction cups over the heating element portion of the heater.

  • Step 2: Set heater temperature: In order to set the temperature, turn the adjustment knob (A) to the required temperature value stated on the graduated scale, located on the top of heater, as shown in FIG 2.
  • Step 3: Heater installation: Install heater in water filled aquarium. The heater works best when installed in the aquarium in the vertical position. The installation of the heater in this position requires that the aquarium must maintain a water level above the minimum water level line (B) on the heater, as shown in FIG 3. The heater can be installed in the aquarium in the horizontal position. The installation of the heater in this position requires that the heater be positioned fully submerged in water at all times, as shown in FIG 3.
  • Step 4: Plug into electrical outlet: Allow for heater to be submerged in water for a minimum of 30 minutes prior to powering the appliance. Once heater has been mounted and submerged for the 30 minutes, plug the appliance into an electrical outlet. Once plugged in, the heater will automatically start working. Should your water need heating, the indicator lamp (C) will illuminate showing that the heater is functioning and in heating mode.
  • Step 5: Adjust temperature: Allow the heater to run for 24 hours at the original setting prior to adjusting. Check the aquarium water with a reliable thermometer. Should the heater need to be adjusted, simply turn the adjustment knob to the appropriate setting.
  • Note: Do not over adjust the heater, this may cause harm to your aquarium inhabitants and environment. Make sure of the required temperature for your specific setup.


Never operate heater without rubber protective guard (E).


To guard against injury, basic safety precautions should be observed including the following:

Read and follow all safety instructions

Danger: To avoid possible electric shock, special care should be taken since water is employed in the use of aquarium equipment. For each of the following situations, do not attempt to repair yourself; return the appliance to an authorized service facility for service or discard the appliance.

  1. A. If the appliance shows any sign of abnormal water leakage, immediately unplug it from the power source.

    B. Carefully examine the appliance after installation. IT should not be plugged in if there is water on the parts not intended to be wet

    C. Do not operate any appliance if it has a damaged cord or plug, or if it is malfunctioning or if it is dropped or damaged in any manner.

    D. To avoid the possibility of the appliance plug or receptacle getting wet, position aquarium stand and tank to one side of the wall mounted receptacle to prevent water from dripping onto the receptacle or plug. As shown in the figure below, a "drip loop" should be arrange by the user for each cord connecting an aquarium appliance to the receptacle. The "drip loop" is the part of the cord below the level of the receptacle, or the connector if an extension cord is used, to prevent water travel along the cord and coming in contact with the receptacle. If the plug or the receptacles do get wet, Don't unplug the cord. Disconnect the fuse to the circuit breaker that supplies power to the appliance. Then unplug and examine for the presence of water in the receptacle.

  2. Close supervision is necessary when any appliance is used by or near children.
  3. 3 To avoid injury, do not contact moving parts or hot parts such as heaters, reflectors, lamp bulbs, etc.
  4. Always unplug an appliance from the outlet when not in use, before putting on or taking off parts, and before cleaning. Never yank the cord to pull plug from the outlet. Grasp the plug and pull to disconnect.
  5. Do not use an appliance for other than intended use. The use of attachments not recommended or sold by the appliance manufacturer may cause an unsafe condition.
  6. Do not install or store the appliance where it will be exposed to the weather or to temperatures below freezing.
  7. Make sure an appliance mounted on a tank is securely installed before operating it.
  8. Read and observe all the important notices on the appliance.
  9. If an extension cord is necessary, a cord with a proper rating should be used. A cord rated for less amperesor watts than the appliance rating may overheat. Care should be taken to arrange the cord so that it will not be tripped over or pulled.
  10. Only For Polarized Attachment Plug Appliances

  11. If this appliance has a polarized plug (one blade is wider than the other) as a safety feature, this plug will fit in a polarized outlet only one way. If the plug does not fit fully in the outlet, reverse the plug. If it still does not fit, contact a qualified electrician. Never use with an extension cord unless plug can be fully inserted. Do not attempt to defeat this safety feature.

Safety Standards:

  • This appliance is intended for indoor household use only.
  • Always disconnect all immersed electrical equipment from power source before placing hands in water.
  • Always maintain adequate water levels as stated in "Set-up"
  • Do not use product if either the cord or the product appear damaged.
  • Do not operate or leave product plugged-in when outside of water.
  • Do not operate the heater without the rubber guard on the bottom of the heater.

Troubleshooting Problems

If problems are encountered:

If the appliance has been installed for 24 hours or more, and the temperature of the water is still much lower than the required temperature, proceed as follows:

  • Be sure to use a quality, accurate thermometer to monitor water temperature.
  • Make sure that the temperature has been set to the correct value.
  • Make sure that the appliance is plugged in and is receiving power.
  • Make sure that appliance is submerged at least to the "minimum water level" line.
  • Make sure the water circulation around the appliance is adequate.
  • Make sure that the volume of the aquarium falls within the range indicated on the label attached to the appliance.
  • Make sure that the glass is not covered with lime scale. If necessary remove scale after the appliance has been unplugged.
  • If the temperature is too high, after the appliance has been working for 24 hours or more, proceed as follows:

  • Make sure that the temperature has been set to the correct value.
  • Check whether too much water has evaporated, consequently reducing the volume to such an extent that it no longer falls within the range given on the label. If this is the case, add water immediately.


This is a common misconception. It is actually water quality that stunts growth in fish, not the size of the aquarium. Since nitrates and other pollutants, which act as growth inhibitors, accumulate more rapidly and to higher concentrations in smaller aquariums, they have a greater impact on fish growth and health in small aquariums. Providing proper filtration and performing frequent partial water exchanges will maximize growth and health in your fish regardless of aquarium size.
Feeding depends on the type of fish you own. Aside from large predatory fish, most aquarium fish do best when fed only what they can consume in 2 minutes or less, once or twice a day. Any leftover food will pollute the water and stress your fish. Herbivorous (vegetarian) fish need to eat more frequently, but still feed only small amounts per feeding. Many experienced aquarists skip feeding their fish once or twice a week to allow them to clear their digestive systems. Watch our short video on the 3 Tips to Succeed to learn about the key tips we recommend in fishkeeping.
Water changes dilute toxins that naturally accumulate in the aquarium. There are many philosophies about frequency and volume, but small water exchanges done frequently are generally considered best for maintaining healthy conditions in your aquarium. A 10% water exchange done weekly is ideal, however, changing about 25% of the aquarium water once or twice a month is sufficient for most aquariums. Avoid changing more than 50% of the water in your aquarium. In doing so you can dramatically change the aquarium water parameters (temperature, pH, chemistry). Major changes to the aquarium environment should be done slowly so fish have time to acclimate.
The frequency of how often a filter cartridge should be changed will vary according to how much waste and free-floating algae is in the fish tank. The general recommendation is to change the filter cartridge once per month.
Filled aquariums weigh approximately 10 lbs. per gallon. For example, a 20 gallon aquarium will weigh about 200 lbs. once filled with fish, substrate, décor and water. Most household furniture will likely only support aquariums of 5 gallons or less. Aquariums that are larger than that should be placed on a stand or base manufactured specifically for aquarium use and designed to safely withstand the weight of a filled aquarium.
Aquariums containing live plants should receive 10-12 hours of high-quality light per day. Tanks with artificial décor only need 5 to 8 hours per day. Hours of light should be the same each day as fish rely on a daily rhythm for their activity and proper health. Use a timer to provide a consistent day/night cycle and never leave the aquarium light on all the time.
Algae is nature's way of purifying water and grows when there is an abundance of nutrients (from fish waste, uneaten food, plant debris, etc.) and light. To keep algae to a minimum, provide proper filtration, feed your fish sparingly, do frequent but small partial water exchanges and avoid excessive light from windows or leaving the aquarium light on too long. Algae eating fish like plecostomus, otocinclus and flying foxes will also help keep algae under control. Watch our short video on the 3 Tips to Succeed to learn about the key tips we recommend in fishkeeping.
There are different views on this, but in general, as long as rocks are sterilized and are not calcium based, you can put them in your aquarium. Scrub them thoroughly and either boil or soak them in a mild bleach solution - rinsing thoroughly afterward before placing them in your aquarium. Calcium based rocks are usually white in color and may raise pH and alkalinity to unsafe levels. They should only be used in African cichlid aquariums. To find out if a rock is calcium based, place a few drops of white vinegar on it; if it fizzes, the rock is probably calcium based.
There are many reasons for cloudy water. Newly set up aquariums may turn cloudy because of a biological imbalance and will usually clear in a few days if left alone. Do not add any new fish or do any cleaning of the tank or filter. Established aquariums can turn cloudy because of overfeeding, too many fish or inadequate filtration. Adding a larger or second filter, removing some fish and/or cutting back on the amount of food entering the aquarium will often resolve this problem. Also make sure that you are doing regular, at least monthly, water changes.
There is no single filter that fits every aquarium need. Typically, hang-on-back filters work well for beginning aquarists because they provide all three types of filtration - mechanical, biological and chemical - and most models use drop-in cartridges, making them very user friendly. Internal filters go inside the aquarium, allowing users to place the aquarium where space is limited. Canister filters can be loaded with virtually any filter media, making them the most versatile type of filter. They take a little more time and effort to service but do not require cleaning as often as other types of filters. Tanks with messy fish should have good mechanical filtration, while heavily populated aquariums should have extra biological media. To ensure optimal performance, choose a filter rated one size larger than your aquarium.
There are advantages to both, and you'll get different opinions depending on who you ask. Glass tanks are more durable, do not scratch easily and because of their strength they can be set on open top stands, which are more affordable. Glass aquariums have open tops, making them easier to decorate and clean. They tend to be more affordable, especially in sizes less than 300 gallons. Acrylic tanks scratch more easily and some may yellow over time. The entire bottom must be supported to prevent bowing and separation of seams. They are lighter and are available in a wider range of shapes than glass aquariums. They can also be easily drilled to accommodate custom plumbing.
Fish don't have eyelids to close, but they do go into a state of rest and reduced metabolism at night, so yes most fish do sleep. Some fish even settle to the bottom at night, and can be picked up by hand. Others remain on alert for danger while in “sleep” mode. Fish that need to keep swimming to breathe, like certain species of sharks, as well as blind cave fish, never sleep.
Actually, the process of “cycling” does not begin until fish or a culture of nitrifying bacteria are added to an aquarium, but the longer you wait to add the first fish after initially setting up your tank, the better. Most aquarium experts recommend waiting at least 48 to 72 hours. Always check temperature and test for pH and ammonia first, as many municipalities add chloramine to tap water and a single dose of water conditioner does not always fully neutralize the ammonia.

It depends on the type of fish you have!

Discus, wild caught angelfish, uaru and certain other fish that are found at or near the equator do better at temperatures between 84° and 88° F.

Betta fish thrive best in water temperatures between 76° and 85° F.

Most tropical fish prefer temperatures ranging from 76° to 80° F.

Goldfish, koi and other coldwater fish prefer the temperatures be between 65° and 72° F.

New livestock purchases should be slowly acclimated to the temperature and water chemistry of your aquarium. Turn off the aquarium light and float the bag containing new fish inside your aquarium for 15 minutes to equalize temperature. Keep the bag closed during this process. After 15 minutes, open the bag, roll the top edge down a few times to form a floatation ring and add a small amount of aquarium water to the bag. Continue adding small amounts of aquarium water to the bag every 5 minutes. After 20 to 30 minutes, gently net the fish out and place them in their new home. Discard the water from the bag, do not pour it into your aquarium. Leave the tank light off for an hour or two to allow the new fish to get used to their new home. An alternate method is to place new fish with their shipping water in a clean container and drip water from your aquarium into the container using air hose and a plastic control valve. Drip rate should range from 1 to 2 drops per second for small bags to a slow dribble for larger bags. After 20 to 30 minutes, gently net the fish out and place them in your aquarium. Leave the tank light off for an hour or two to allow the new fish to get used to their new home.

No, simply seeing condensation inside your Aqueon Glass Adjustable Heater does not that it is broken or defective.

Check that the heater is working properly by using a thermometer with your fish tank. (also make sure that the water is the right temperature for the type of fish that you have inside your fish tank)

The reason you may see condensation is because humidity was in the air and trapped inside the tube when it was manufactured and sealed. Your heater is still able to perform properly with this condensation.

Customer Reviews

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100% Recommend this product (1 of 1 responses)
By uni
Steady Temp Keeper
May 9, 2016
It is keeping a nice steady temperature in my fifty-five gallon tank. My fish are grateful for a heater that works well, especially the ecstatic Mollies who demand their water-bed warm. The Bushies immediately laid lots of eggs and the babes are surviving better than ever before due to steady temperature. I've had a smaller heater in my twenty gallon baby-tank for a long time, and I MUST sell babies soon for there are so many. Of course my tank filters function well with steady temperatures also.

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