Absolute minimum, like 10% or less if you are going to follow the philosophy to the letter.
Have a read through the algae vs ferts vs light thread in here and see Jennifer's advice to me in particular. I have low lighted times and low light plants, the hair algae in my planted tank was at its least when I changed little or no water. You will pretty much just have to wait till everything has settled in and experiment and see what likes to grow under the conditions you provide and how to combat any algae that starts to compete with the plants. Low light can mean slow growing plants meaning that nutrients are left in the water column for the algae to chomp on.