I have 1x 55w PC 10k on my planeted 25gal. I do zero suppliments, no CO2 .. nothing.. the plants get over grown within a week. I have one that is actualy blooming right now.
At one point I did the DIY CO2. It seemed to help, had the little O2 bubbles coming off the plants, always a good sign. But the growth rates were about the same as it is now with zero CO2 additions.
Just my thoughts..