It's ready when the leaves are soft and squishy. Drain and cut it into little pieces. Feed a pinch every day.  Other types of lettuce should work too. However, only use softer leaves. Also, all pieces should be small enough for their tiny mouths. Tadpoles can also be fed normal flake fish food but only in small pinches, as it's not the absolute best for them. A couple of pinches a week should keep the tadpoles hunger satisfied depending on the number of tadpoles you keep. Too much food can cause death to the tadpoles from over-eating.

TL;DR in Chinese:
将莴笋叶子煮10到15分钟。