Bala sharks??

could i do like 1 red tail in the 10?

You could probably get away with that. They can be territorial. If your plan is to have just the 1 fish, I think it would be ok. Just give it something like a cave area to call home and it should be content with its new home.
 
There really is no such thing as a freshwater "shark". They are actually a type of catfish and as such do get quite large. The iridescent shark gets even larger yet!

I agree that the Iridescent shark is a type of catfish (Siluriformes), but the other 'sharks' (the Bala, Redtail, Rainbow and Black) are not. They are (Cyprinids) and are related to the Barbs, Danios, Loaches, Minnows, Rasboras, Carp, Goldfish, etc.
I'm not pickin' on ya excuzzzeme, but I just had to clarify that. :)
 
I personally have never seen a 6" RTS, however I do think they need more space than 10 gallons, even alone.

I have a 6 inch rainbow shark in a 75 gallon. It's super active and I wouldn't keep it in anything less than a 3' tank.
 
Maybe you should look more to schooling fish?
 
I would not recommend getting anything labeled shark for your tank. Most of these get quite large, as has been mentioned. If you want something like them, you might consider pygmy corydoras, a group of 5.

A 10g tank is not appropriate for most common fish, thought it seems to be one of the most popular sizes for tanks. Ironic, isn't it? Other options for your 10g tank are as follows:
Option 1: A single betta with some snails and/or shrimp (betta might pick on/eat the inverts though).

Option 2: A single kribensis with snails.

Option 3: A group of pymgy corydoras (no more than 6 but must be at least 3).

Option 4: A group of 6-10 small schooling fish like neon tetras.

Option 5: A single ram (these can be difficult for beginner aquarists, though, as they are sensitive).

Option 6: A group of about 7 boraras urophthalmoides (exclamation point rasboras), a very small fish

Option 7: Least killifish (not sure you could have, experts?).

There are more, but I can't think of them off the top of my head right now.
 
E things with sharks is they need the length for "pacing" although I will say I have a RTS in my 55 and only uses about 15 gallons worth of space, but all fish are different
 
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