Yeah I'd shoot for 250 minimum. I've never kept maximas successfully in the LED era until I kept this current one at 250+. It stopped growing at 150ish and looked sluggish, then I bought it up to 250 and the growth came back quickly. Definitely recommend the Fatheree clam book too!John from Clammania says the safe zone PAR for clams are:
However, the more PAR the better as long as you acclimate them to higher PAR, you can also bleach clams. Also keep your water quality good and you won’t have to feed them. I currently have a 2” Crocea at 250 PAR and have noticed the growth.