JBL ProTemp e500 In-Line Aquarium Heater is the higher output in-line heater in JBL's ProTemp range, fitting into the hose of an external filter instead of going inside the tank.

Key Features

• Nothing visible inside the tank: The heater sits in the filter hose inside the cabinet, so there is no glass tube stuck to the back pane and nothing to hide behind planting. On a display or aquascaped tank that is the whole point of it.
• Even heat, because it heats the flow: An in-line heater warms the water on its way back to the tank, so the heat arrives already mixed through the return rather than forming a warm pocket around an element.
• Fits the common hose sizes: Supplied with interchangeable screw-on connections for 12/16, 16/22 and 19/25 mm hose, which covers the whole CristalProfi external range and most other canisters.
• Holds to half a degree: JBL quote an accuracy of plus or minus 0.5 degrees, which is tighter than most internal heaters manage and tight enough for marine and for sensitive soft water species.
• LED display on the unit: The set and actual temperature read off the body of the heater, and it switches on a one degree interval, so you can see what it is doing without guessing from a dial.

Fitting An In-Line Heater

• The heater goes into the hose of an external canister filter, so you need one. There is no way to use an in-line heater on a tank running an internal filter.
• Cutting the hose is not reversible. Work out where the unit will sit, allow for its length, and cut once.
• Fit the adapter that matches your hose. Screw-on connections for 12/16, 16/22 and 19/25 mm are included, which are the same sizes the CristalProfi externals use.
• It only heats while water is moving through it, so it must be on the same supply as the filter. If the filter stops and the heater does not, it is heating a static column of water.
• Mount it below the water line alongside the filter, and check both connections for weeping twice before you close the cabinet. A leak here is a leak inside the cabinet.
• Tighten the collars by hand only. Overtightening cracks the plastic, and that is a leak you will not notice until the floor is wet.

Heater Safety

• Switch off at the wall before you open the filter or work in the cabinet. This is a mains powered heating element sitting in a water line, and it is the one piece of aquarium equipment where that matters absolutely.
• Unplug the heater whenever the filter is off. It is only safe while water is moving through it, so it should never be running on a stopped filter.
• Heaters usually fail stuck on rather than stuck off, and a thermostat that sticks closed will cook a tank inside a day. That is why an independent thermometer, checked daily, matters more than any heater's accuracy figure.
• Do not fit more wattage than the tank needs. An oversized heater stuck on raises the temperature far faster than a correctly sized one would.
• Because it lives in the cabinet, a fault here is out of sight. Check the body and both hose connections for weeping, scale and discolouration every time you service the filter.
• An RCD on the aquarium's supply is a sensible precaution on any tank with a heater in it.

Heating A Tank Here

• In an air conditioned room a heater has far less work to do than JBL's European figures assume. A room held at 22 to 24 degrees with a tank wanted at 25 or 26 needs very little input, and the heater will spend most of its time switched off.
• The real risk in this climate runs the other way. A tank in a room without air conditioning can climb well past the safe range in summer, and no heater helps with that.
• If a tank sits above about 28 degrees, the answer is cooling rather than heating: more surface movement, a fan blowing across the water, the lid open, a shorter lighting period, or a chiller on a marine or discus tank.
• Warm water holds less oxygen, so a tank running hot needs more aeration rather than less.
• Think of the heater as a floor rather than a target. Its job is to stop the tank dropping when the air conditioning runs hard overnight.

Good To Know

• This is the larger of the two in-line heaters. JBL rate the e300 for tanks up to around 300 litres; send us your tank volume and we will confirm which of the two suits it before you order.
• You need an external canister filter to use it. On a tank with an internal filter, look at the ProTemp S internal heaters instead.
• On a large tank, running this alongside a smaller internal heater gives you a margin if either one fails.
• Keep a separate thermometer in the tank and look at it. It is the only thing that tells you the heater is still doing what it says it is doing, and it costs very little next to a tank of fish.