Sea Lettuce (Ulva lactuca) is one of the more nutritious macro algaes, and is readly eaten by tangs, angels and other herbivorous fish. It is very quick growing and as with most macro algaes, it does best in a refugium where it helps reduce nitrates and phosphates. It prefers strong lighting and a higher flow (moderate to high). It can also be tumbled gently with air stones. 
 
Small - Baseball size
Medium - Softball size
Large - .5 lb (2 Softball size portions)