I started using glut in my tank again and within a week my glass is basically spotless, leaves are getting very close to spotless, and already looking fuller, wider, more dense. Water column is clearer. Fish seem to be more active. I won't pretend to say it's providing carbon, but it is wiping out micro algae that allows the plants to absorb more light and take in more nutrients/co2 from the water. Shit works great.
Metricide 28, a gallon off ebay is $23-28, lasts several months (toss the small activator bottle that it comes with in the trash). 10mL every day initially, then every few days (65 gallons, probably works fine with less). I use a syringe from the baby isle (used for squirting medicine). It's effectively medical grade Seachem Excel. Don't get the shit on your hands or breathe it. Reacts quickly with algae so you can stick your hands in the water after a couple days. Doesn't kill off beneficial bacteria, because the nitrogen cycle isn't affected.
Anyone else ever used PPS Pro from Greenleaf Aquariums? That shit will make your plants take off. Macro and micro nutrient liquid dosing.