No they are not.
no \
By keeping it in a sealed container with the same temp at all times.
no
Yes, red algae and red marine algae refer to the same group of algae that are predominantly found in marine environments. They are known for their red pigmentation due to the presence of phycoerythrin pigments.
No they are not the same
Protists in the supergroup Archaeplastida are in the same eukaryotic supergroup as land plants. This supergroup includes red algae, green algae, and land plants, which all share a common ancestor that underwent primary endosymbiosis with a cyanobacterium.
Yes two Algae (a kind of primitive plant life) can be (develop) in the same tank. There is no reason why they should not.
Algae
The same way all other fish eat? Algae, other fish, etc.
Many but not all algae is multicellular.
Plants and green algae both have the same types of organelles. This is because they both are able to create their own food.
Thousands and Billions of species of algae is not discovered.