My 29g has 72watts of CF
lighting over it (certainly more light in the tank than you described).
I am using an Au natural method on this tank. It gets no ferts except for 1 tsp of Equilibrium at water change. And water changes are once per month. The tank has tons of shrimp and tons of snails... but only about 6-8 inches of fish. I feed it fairly heavily.
Anyways, this tank has no real algae issues. It slowly gets some GSA, i only clean it every 2-3 months so its not that bad.
I am a proponent of EI, and use it on my high light tanks. But anything less than 3wpg (of high quality light) and I just let the tank be.
Interestingly enough, I am about to set up a row of tanks in my garage much as you have described.
I am going to line up the 10g's on a shelf and put a regular shop light over them (2x 40w). They will be planted with crypts and moss, they are for my wife Guppy breeding. She has a strain of Japanes Blue endlers. I'd show you a picture of these lovely fish, but guppies are only a colorful blur on my old camera.
I was just thinking back to my old Shrimp tank. It had 30w (2x 15) over 10 gallons. It grew a ton of plants and no algae. No ferts, no CO2