Low Tech, Low Light Tank Ferts
Hello Jessy. I can only tell you what I've found after a few years of keeping low tech (no CO2), low light tanks. I have less than 1 watt per gallon for lighting and keep several large well planted tanks.
Plant a lot of stems like Water Sprite, Water Wisteria, Rotala and Ludwigia. These do well, as they grow toward the light. I also have a lot of Java Fern, Crypts and Anubias. Any of the mosses will do well in low light too.
Tropical plants in low light conditions, need a good liquid fert to do well. I rotate using several kinds of liquids simply because plants, like all living things will do best if fed a varied diet. I currently use Yamato Green. It has all the nutrients plants need. I just add a capful to a pitcher of my water change water and dose when I need to top off the tanks, usually two to three times per week.
Since you have Vals, avoid using Seachem's Flourish Excel.
You can have well planted tanks in less than one watt per gallon conditions. My lights are 6,500 K T8s and T5s I get for a few dollars at the local Lowe's and have one tube per tank.
Just let me know if you have any other questions.