From the sounds of it you are doing a low density culture in that 2.5 tank. Phyto Feast would be too expensive to use for dense culturing.
I've not had a brown algae form in my containers, especially so soon after starting the culture.
IMO it's bad to have started the culture in the tank and apparently continue the growout with the same water. Empty or unhatched cysts or membrane residue congealing may be what you are seeing. Algae is unlikely to have grown that fast.
Are you using standard cysts or decapped ones? How many cysts did you put in the 2.5?
You need to hatch out in a hatching container (
http://www.angelfire.com/ab/rayjay/Hatcher.html ) and then separate the live nauplii from the empty and unhatched cysts, or cyst membrane residue in the case of decapped before adding to the growout tank.
I'd recommend treating with peroxide first if you are using regular cysts.
As the nauplii grow and progress through the molts, you will end up with a lot of garbage in the container that comes from the molts and from feces produced. This turns the water brown and needs to be cleaned up as it gets bad because the brine will feed on it also, thus lowering the nutrient value of them.
I let the container sit so anything not live settles, and then siphon off the live brine, clean the container well, and then replace using new water. Cleaning interval depends on your set up and the density of the culture, and even what foods and how heavily fed the brine are so it's not a fixed thing for each hobbyist's set up.
I made a net from Brine Shrimp Directs 150 mesh bag (can make 2 per bag) and sit it in a larger mesh net that is siliconed half way up. The larger mesh net holds enough water then when siphoning to help cushion the brine as they get siphoned into the 150 mesh inside the large mesh net. (Hope that makes sense for you)
Unfortunately you still get some garbage that doesn't pass through the mesh, but as the brine grow you can use a larger mesh for later cleanings and the garbage will all pass through.
I wouldn't consider putting anything like stars or snails into the culture and don't feel it is going to help you any, and indeed could be a source of pathogens being introduced to the culture.