Stocking my 30 Gal

[Mystic Fish]

The bioload difference between 4 and 6 isn't substantial, and I always recommend 6 of each species of tetra. If you could do 6 Rummys and 6 Cardinals, you'd have a nice group of shoaling tetras that would often school tightly.

I would rather 6, but im thinking about the space in my tank... it isnt long. See the pics in 1st post

 

[Mystic Fish]

Another 6 is fine for my tank? (tall tank)

 

[PNWaquarist]

I'd run your tank's dimensions and stocking through AqAdvisor.com.

 

[Mystic Fish]

Here it is

But does it take into account that my tank is tall (less swimming space)

EDIT: Or i could do this but its hard to keep an oto alive for more than a month

 

[PNWaquarist]

Yes, it does. You're good.