The red tail shark is not a real shark, its just called that. I plan on getting a crab and an algae eater. I need something that adds more color... Any ideas about what to get?

Tiger barbs are too big too aggressive and too active for a tank this small.

Any freshwater fish with the term shark in the name is no good for such a small tank. Redtail grows over 6 inches long and can be territorial.

Crabs eat fish.

Algae eater is not a kind of fish, but most fish that are called this need a bigger tank - in fact, many of them are not even really algae eater. A common pleco grows to over 2 FEET long.

So far the only decent thing mentioned is the platys.

Fish for a small tank must be small. Pygmy corycats, kuhli loaches, ember tetras, betta, sparkling gourami... These types are more what you should look at.

The barbs will bully the platies. And I think the barbs need more room than this(google). Get a 20 gal. And the red tail shark needs a way bigger tank (I won't even bother to explain this time, just google how big they get and how big the min tank size has to be). Return it along with the tank to get a bigger tank. Next time you go to the petshop, run away from anything which has the word "shark" in its name unless you have a 100+gal tank (my policy). pets question and answers,www.5d2d.com
Or change the stock to all platies or other small community fish.
A)5-7 neontetras/platies/guppies/harlequin rosaboras
B)1 male betta
C)5 female bettas
D) 1-2 honey gourami/dwarf gourami/ sparkling gourami (you can get 2 if your tank was bigger or else they'd bully each other).
Choose one choice and add up to 3 small loaches/cories which would live in a 10gal or get a few ghost shrimp and snails if you have plants.

And no crabs. You're already overstocked.

Next time you try with fish, do some research. The most common problem with beginners starting fish keeping is overstocking. Fish need space. Appearances can be deceiving. Really small fish can get huge and many petshop people don't know what they're doing or don't care if these fish get the right care needed or not.

tiger barbs can get aggressive with other fish keep an eye on them

Your red tail shark is going to get large, and probably aggressive too, so a 10 gallon is a no no for it. Tiger barbs need a school of 6 or more, or else be prepared for dead/injured fish. 2 platys is ok, I guess. Crab in any given chance or opportunity will kill and eat your fish. Algea eater, majority of it will out-grown your tank.

pets question and answers,www.5d2d.com

I'd say either get more tiger barbs, or remove them and get danios, neon tetra, etc.