Was your tank established prior to the plants? I imagine it is was because of the discuss but High Nitrate in a planted tank is definitely not the norm rather we usually have to add it to keep the plants happy.

I am guessing your method of CO2 probably isn't the most effective so unless you want to invest some money I would start by reading the "Non CO2 methods" article. That will let you know the ferts you need.

As for lighting period I believe 10 hours a day is pretty standard but peoples opinions vary. I have no idea if you have adequate lighting though with the info given.

If you are having issues with nitrate you could try throwing some Hornwort in there as it eats nitrate pretty quickly and is undemanding. It's a floating plant so you can keep the bare bottom without anymore pots.

What plants do you have now?