Sea lettuce turning white - bad?

[KCD1803]

Got some sea lettuce and the surface is getting some white on them, good/ bad / indifferent?

can post pic tonight

 

[phobos2deimos]

My Ulva seems to thrive in waves, one month it's great and then a week or two of crummy. I started keeping my phosphate levels higher (~.5-1ppm) and it really took off, but then this week it started crapping out again. Might be your phosphate?