Unless someone else suggest it's not, the Planted+ is adequate light for that tank.
You have only a small amount of the necessary nutrients going into the tank for the
plants/w SC Flourish. I will provide a link to a thread which explains this well.
You only need to read the introduction post. Not the whole thread.
You also don't need to use the "EI" type of fert system because it is designed for a high tech tank environment and you have a low tech tank environment which uses less ferts.
Adult people just maintain, but children grow. Just like them, plants need all of the necessary food (ferts) in order to grow.
I will also give you a link to a for sale thread in which is ferts in several forms.
I would not buy any but one just yet as you need to learn a little about the whole thing first. But I will suggest that you buy some Osmocote+ capsules from him now.
The cost including shipping is minimal. You only need 5 of them for a 55g tank to
be placed in there and they will last for about 5 months.
After you learn a little about the ferts then I suggest you use this part of his list.
That one order will get you enough for almost a year, but the next time you need to refill it it will only cost $12 plus the shipping for the next years supply.
"PPS-Pro Liquid Ferts"
PPS-Pro style liquid fertilizer- $27 shipped
-2x 500ml dosing bottles
-Pre-measured micros and macros, enough to dose 5000 gallons of tank water.
-Also comes with set of refill packets
Additional refill Packets are $6 per set.
The ferts will come already in the dosing bottle, simply fill the bottle with 500ml of RO water and you are ready to go.
Dose 1ml per 10 gallons of water of each micro and macro ferts each day prior to lights coming on.