Heat Cord ThermoSub 100w Heating Cable. Substrate Heating Cable 100w. Recommended for use with a thermostat. Suitable for use in a tropical aquarium or a planted tank. The recommended minimum tank size is 120L. The heat cord ThermoSub 100w heating cable is 5.5m long. ThermoSub heating cables are designed to maintain a substrate temperature that is higher than the water in the aquarium. This helps to increase plant metabolism, which increases the uptake of nutrients. Additionally this results in faster growth and less excess nutrients in the water column. Using the thermosub heating cable will create convection currents through the substrate. This helps bring nutrients to the plant roots rather than the leaves, as the nutrients are more readily absorbed in the roots. Instructions are also included. Other sizes are also available: Heat Cord ThermoSub 25w Heating Cable Heat Cord ThermoSub 150w Heating Cable