I bought a 24 watt unit a few years ago and it has worked great. He cleared my tank of green floating algae in 4 days. I left the machine on even though the water was crystal clear. The UV lamp lasts 3-6 months. Replacing the unit and replacement bulb is expensive, but you really don't have a choice. I recently bought a new block for my 55 gallon tank. I will not leave the device on all the time. Overall, I can recommend this product and give it 3 stars. Again, this works great, but it's expensive.
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