I bought two of these for my 30 gallon tank. There wasn't enough of it to cover all of this. In addition, only a month has passed and one of them has already burned down. The one that's still running is fine. I use it about 8 hours continuously a day. Though I was hoping the light would be stronger. I would say two would be enough for a 20 gallon aquarium. The rating should be 3 stars for a lamp that is still working and 1 for a lamp that has already burned out.
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