I understand not wanting to add any equipment into the tank. On my 30 gallon I have two DIY Co2 bottles going, they each run into powerheads on opposite sides of the tank. At first I was annoyed that I had these 2 hunks of plastic in the tank, but they do great to defuse the CO2-I have the CO2 going into the intake of the powerhead (also a sponge over the intakes so they won't get clogged), I also cut a little piece of sponge and put it on the output of the powerhead, that seems to help break up the Co2 bubbles even more. Once I saw how good the powerheads were at diffusing the CO2, I got past the equipment in the tank...I just hid them behind some steam plants....maybe you could hide the powerhead behind the driftwood on the left?
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