undergravel heater?

Under Gravel heaters can be of great benefit, to opften a standard submersible heater will only heat the surrounding water and temperatures measured below the gravel can be considerably less, some plants such as crypts prefer the substrate to be heated this helps to greatly encourage root growth and allows for better nutrient uptake due to increased surface area achieved.
 
seems like it would be a big hassle getting them untangled from roots and whatnot as well.
 
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