Salut,
J'ai trouvé ça sur le forum APC à propos de cette plante:
"This Ludwigia makes several demands on the hobbyist before showing its full potential such as intense lighting, CO2, a well balanced nutrient regime, and space. However, when conditions are good, this stem plant grows rapidly. Intense lighting is necessary (aim for at least 3 watts per gallon). CO2 supplementation is a necessity; without it, this plant develops broader, greener leaves, produces fewer leaves per whorl, and grows more slowly. Nitrate (5-15 ppm) and phosphate (1-2 ppm) supplementation through the water column is necessary for good coloration and health. Heavy iron and micronutrient fertilization with a reliable liquid fertilizer is also necessary for this species; if new growth is white, this plant is not receiving enough iron."
Moi sur un bac de deux semaines j'attendrais également avant de m'inquiéter. Après si ça persiste et empire peut être mettre un peu de Fe et observer les nouvelles pousses.