In my 10g tank Lud. Repens used to grow very fast, now it hardly grows at all. Sunset Hygro and Green Ludwigia are growing well. I am starting to do water changes for the first time in an attempt to revive the red ludwigia, and to replace whatever nutrient it's missing, as I've also recently stopped adding micronutrients as I think the iron was causing algae. My bulb (11W - the same as in my desk lamp) is a year old now and probably needs replacing.
My Sunset hygro and Large ambulia get better growth (much shorter internodes) than in my 75g tank where the Ludwigia (both type) grow fast. (That tank has eco-complete, bottled CO2, still only 1wpg lights but the type of light tubes that don't lose much power with age, apparently.)