You can bump up the co2 with another liter and place a airstone in just as a precaution to get rid of that algae. Or you can leave it as is, and just decrease the amount of time your light on by an hour, if that doesn't work, cut the time back again.
I saw a significant increase in plant growth and reduction in algae once I started diffusing co2 through a hagen mini underwater filter. I spent $15 because I paid for shipping on the filter. You might be able to find something locally. A small powerhead would also do the trick.
I was originally putting diy co2 straight to the HOB filter intake. Even with an airstone I noticed a whole bunch of co2 gassing off inside the filter.
You may have better luck in your tank because my water is pretty hard thus reducing co2 absorption.