un or algun?

Hola Ricky

Most of the time unos and algunos are interchangeable. However if we mean "some" as in an approximate quantity of something we use "unos" not "algunos". For example "Vendimos unas 30 camisetas en el mercado." (We sold "about" 30 t-shirts in the market.) (We wouldn't use "algunas 30 camisetas...here). 

Also, if it is accompanied by "de" as in "some of [noun]..." we would use "algunos" not " unos. For example: "Algunos de nuestros amigos son muy irresponsables." (Some of our friends are very irresponsible.) (We wouldn't use "unos de..." here.)

I hope this helps.

Inma :))