you need about ten to 12 hours of light for plants. flourish seachem has phosphates, I don't use it for that reason because you'll build up plenty of phosphate without it and that will mean algae. You can rig a DIY CO2 system using pop bottles with sugar,warm water, and yeast, airline, and air bubble ladders you can buy. I have three on a 78 gallon tank and they work just fine. you just have to change the yeast mixture every couple weeks, staggering which bottle you change so you have a steady CO2 level.
you can also use Flourish Excel as a carbon supplement that helps with CO2 levels.
82 is a little cool if they're young discus.
and two discus is not enough. six is the minimum recommended in a tank.
there are lots of plants that do well in low to medium light... you could go browse the tropica website to see some you might like.
most popular are amazon swords, anubia, cryptocorynes, watersprite, vallisneria, pennywort, hornwort, lots of different types of stem plants.