Hi Alvin,
(1) macroalgae: There are several types, the most common being C. racemosa -looks like bunches of grapes n can morph into oarlike shape. Usually available from Pinnacle, Ah Meng n Iwarna. Has a tendency to collapse n turn the water milky if conditions r not suitable.
C. sertularoides --feathery-like like coconut leaf fronds. Prolific grower n rated a nuisance algae in the U.S. where large areas have resulted in local algae being killed off. BTW they r inedible unlike racemosa. Curretly Iwarna grows the C. mexicana below their hanging algae filter. Just to name a few from the long list.
(2) Halimeda is a calcareous algae like little prickly pear cactus. Most attached to the mushrooms on rocks u buy. Never seen any for sale 'cos they come foc.
(3) Bubble algae will bloom in ur tank if the water has high nitrate. Lords knows where they come from . It's considered a nuisance algae.
(4) Sargassum can be easily obtained from the breakwater at the East Coast Park, at low tide n washed ashore. U'll need MH to keep them alive. N
the naso literatus is very fond of eating them. A natural source of algae feed.
All things said, Ah Meng nearly always have algae on rocks of a few species for sale.
Hope the above info is useful to u.
Once n algae breeder,
Finbir.