The substrate heating
The heater that doesn't heat but flushes - all for the benefit of the aquarium plants
With a substrate heating you promote the growth of your aquatic plants enormously by creating a water circulation in the substrate, which washes nutrient-rich water directly to the roots. A substrate heating consists of a long heating cable which is laid in curved lines on the bottom panel of the aquarium. The water heats up directly at the cable and rises upwards. Cooler water starts to flow between the cable loops, creating a water circulation in the bottom area which permanently washes nutrient-rich water to the plant roots. Only very fine substrates (fine sand) might prevent a sufficient water circulation for a substrate heating. In this case heat is very likely to become trapped at the bottom, which is not ideal. That’s why undergravel heating cables are only suitable from grain sizes of around 0.8 mm onwards.
A substrate heating is not meant to heat your aquarium water, it only serves as “micro circulation” in the bottom area. Therefore the wattage of the undergravel heating cable is significantly lower than that of heaters. You can read how to install a substrate heating here: Installation technical items .
Which wattage is right for your aquarium?
If you look on the packaging of the substrate heating cable JBL PROTEMP b III to find out which aquarium size the heating cable is suitable for, you will see a wide range. For example, the smallest substrate heating cable, the JBL PROTEMP b10 , is marked 40-120 litres. The number of litres is actually not the decisive factor, but the area on which the substrate heating is to be laid out! That’s why it says 40-80 cm under the number of litres. In a 40 cm aquarium, the length of the substrate heating cable (e.g. 3.6 m for the 10 W version) would be sufficient for the entire substrate. In an 80 cm aquarium, the loops of the heating cable would only cover part of the bottom pane. This can actually be quite useful as lots of aquariums only have plants in the rear part! So before laying the substrate heating cable, think through where the plants will be and only lay the substrate heating cable there. Aquarists who have covered the entire front part of the aquarium with grass plants will usually have to refer to the smaller aquarium size on the range specification.
It’s perfectly normal for the wattage of the substrate heater to be much lower than the wattage of your heater thermostat. The heater thermostat (e.g. JBL PROTEMP S 25 ) is designed to bring the water temperature of your aquarium to the correct value for your fish species, e.g. 25 °C. The substrate heating cable, on the other hand, is only intended to heat the water right at the cable so that the heated water rises and creates water circulation in the substrate. Very little energy (watts) is needed to create this water circulation.
What’s important when installing a substrate heating cable?
First of all, there is the timing: the installation is only possible with an empty aquarium. Try to stay calm if your pet shop salesperson decides to recommend a undergravel heating cable after you have bought your entire setup equipment from them.
BEFORE you lay the cable in loops at the bottom of your aquarium, consider which areas you will plant. You’ll only need the heating cable in these areas.
And you’ll probably intend to put a long-term plant nutrient substrate ( JBL PROFLORA AquaBasis plus ) above the heating cable. Later, when you clean the ground with a substrate cleaner (gravel cleaner: JBL PROCLEAN AQUA EX 10-35 ) and plough the substrate to suck out the dirt, you won't want to pull out the nutrient substate again or get caught in the undergravel heating cable. SO only place the heating cable and long-term nutrient substrate in the planted areas.
The undergravel heating cable consists of a cable part that does not heat up and a part that does. The "cold" cable part should end where the cable enters the substrate.. Only the part of the cable under the substrate needs to heat up. You can identify the transition from the part that remains cold to the part that heats up on the JBL undergravel heating cables ( JBL PROTEMP b III ) by the black marked part of the heating cable.
It’s perfectly normal for the wattage of the substrate heater to be much lower than the wattage of your heater thermostat. The heater thermostat (e.g. JBL PROTEMP S 25 ) is designed to bring the water temperature of your aquarium to the correct value for your fish species, e.g. 25 °C. The substrate heating cable, on the other hand, is only intended to heat the water right at the cable so that the heated water rises and creates water circulation in the substrate. Very little energy (watts) is needed to create this water circulation.