red algea?

they're different organisms. red algae are rhodophyta, green algae are chlorophyta (I think), brown algae are usually diatoms. that it changed means that something changed in your tank, and it now favors the red kind over the green. this could be anything from light, to nutrient levels, whatever.

i don't know if it's just green algae that died, though. I've never seen that happen in my tanks.

i've never had red algae, but I hear it's nasty and hard to get rid of...