So, Corkscrew Val...

I have them growing in less than 1 wpg and I have to thin them out every couple of weeks.

It depends on the type of lighting and how tall the tank is rather than wattage and water volume.

For example, 36 watts of T5HO lighting over a 20g long tank will have more lumens available to the plants than 48 watts of T8NO lighting over a 20g high tank.

So really the best way for us to answer is to know what sort of tank you're growing them in, and what kind of lighting you have.

I have spiral val growing in a moderately planted 20G High.
Lighting is 2 23W Daylight Spiral CFls in a 'reptile light' fixture with a metal reflector.

It's doing fine and reproducing, but not "going nuts" in there.
No ferts or CO2, just fish poop.