I was surprised at how powerful they were for the stated power. Especially 20 watts. I ended up using a 20 watt heater connected to an ink bird controller in my Fluval Spec 3 as it was too powerful for my Spec 3 as it was an "always on" heater . She was even too strong for my 10 gallon FijiCube. beta tank. 10W heaters work well as secondary heaters.
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