2x39w on a 40b is really pushing it on needing pressurized co2
and ferts IME. 4x39w is really hard to control until you get th right balance. I grew all kinds of plants in my 40b with a 2x39w. Once I switched to 4x39w, I grew algae with no problem. The plants grew too, and I eventually found a balance that worked well for me. I'd stick with the 2x39w until you're ready for a high tech tank.
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