I have algae!

how long has the tank been up?? Brown algae is common with new tanks where silicates are higher than normal.

I think you would also be fine shortening your lights on time to 8 hours. Also get your CO2 back on and stick with it. I think that consistency is really the best way to combat algae. Any pics of the algae would help to determine any causes.

Are you using any ferts and what are your other water parameters, NPK, ammonia, nitrites etc?

I occasionally get a bit of algae in my planted tank. My solution is to scale back the ferts for a week or two while keeping everything else consistent. The first time I identified it as a problem, I cut off the ferts completely until the algae was almost gone, then started them back up with a half dose the first week, then 80% the next and a full dose the third. Now I cut them back about 10% when the algae first appears and it's been working like a charm for me. But my planted tank is also a live-fed predator tank, so the algal cycle is largely dependant on the feeding cycle. My answer isn't likely the answer for everyone, but it works for me in my specific instance which is really what fishkeeper's problem solving is about: no static answers, just what works for each specific and unique situation.