yes you can feed your growing plants from your fish tank
and return the same water to it!. what you cant do is add specialist nutrients, these are detrimental to the fish!, and will cause masive algae blooms!,,, i have a friend who runs a display unit in the shop using this method!,,,,however i do not knw what if any controll you would have for flowering!!,,,,,
by the way i love the sound of your tank,,, it was aquarians that got me into hydro! i used to grow and feed tropical plants by feeding the sollution to a tray above the tank and at the same time made a natural filter using stones plants with arial roots etc,,,
another great hobby...with endless possibilities,,,, i ended up with 15 tanks of varieing sizes, and lots od cichlids
hey good luck!
and welcome to the world of endless possibilities,,,,,hydroponics