Understanding balance of a planted tank is the key to success. It all starts with the light. The more light the faster the plants will grow therefore more demand for nutrients and carbon dioxide.
First off ditch using those KH/PH charts. They are completely useless.
You need to take some tank water and aerate for 24 hours and test pH. You then need to test pH directly from your tank at the end of your photoperiod. Compare the 2. The tank with CO2 injection should be 1 degree lower. If your pH is 7.6 then you want to aim for 6.6.
Reduce photo period to 6 hours for now. Then remove as much algae as possible, even if it means doing some trimming of plants. Perform a 50% water change after. Start double dosing with Flourish Excel for a week.
Now, your fertilizers. Zero nitrAtes is a bad thing in a planted tank. You want to aim for 10-20 ppm of NitrAtes. This is a necessary macro nutrient for plants. You need a Nitrogen Supplement if you can find one.
Potassium (potassium deficiency are pinholes in leaves and sometimes curling leaves)
Phosphates (lack of PO4 can be Green Spot Algae showing up)
Micro Nutrients also known as Trace Elements:
Magnesium, Boron, Manganese, Iron, Copper etc.
Check your current Fertilizers. They most likely may only be Micros.
What is your GH reading? This tests both Calcium and Magnesium. If your Mg. is low then adding Epsom Salts will help; Magnesium Sulfate. Signs for deficiency are leaves will have yellow patches/green veins. Almost like Iron deficiency.
You need to make sure you are providing all of these necessary nutrients and that your CO2 is efficient. Sounds like you have an issue with imbalance with CO2/fertilizers.