2 more lights for tank?

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Hi all,

 

I have the oppurtunity to borrow a buddy's lights system for the rest of the year. I currently have 2 florescent lights - actinic + marine (can't remember the makes). He has the same bulbs. They are all 15W lights. So, if I put them on my 15Gal, I would go from 2 Watts per gallon, up to 4 Watts per gallon. I assume it's a significant improvement?

 

I plan to get a 50 or 100Watt Metal Halide at the end of the year - December bonus - so don't want to spend more cash now.

 

Thanks