At the moment i have 5 danios, i'm thinking of introducing around 7-8 cardinal tetras. Would these two get along or would the danios just hassle the cardinals? btw my tank is 125l
I see no problems with that. The danios are very active, so you will have to make sure the cardinals get some food, but other than that it should be fine.
How long has your tank been set up? I wouldn't recommend cardinals if your set up is less than 3 months old.