Ay, dark green poop sa 9 months old can be normal talaga, lalo na if baby's eating solids na and masyadong maraming iron-rich foods like spinach or fortified cereals, a few of my mum friends noticed yan din sa kanilang babies around that age! But honestly, since you're worried, mas better to check with your pediatrician lang para sure, especially if may other changes like diarrhea, constipation, o kung parang uncomfortable ang baby, kasi sila lang talaga ang makakasabi ng tama based sa overall health ng bubs mo. Trust your gut as a mom, walang masama sa pag-follow up, yan ang ginagawa namin palagi.