Wow, thanks for your replies everyone!
I had danios in this tank a while ago and I agree that they need more space as the 2 I had were quite aggressive (unless they're always like that?)
Also I'm aware how big those bristle nose get! My boyfriend loves them and has quite a large one in his (massive) aquarium, I plan to give it to him when it grows
(it's only the size of my pinky atm).
And thank you for all your fish suggestions! I'm thinking I'll stick with my guppies though ( they're cycling it now) and get maybe 4 or 5 neons. I've had the neons before in this tank and they lived for manyyyy years! I don't have a lot of obstructive decorations either just plants so they dart around quite freely.
My tanks exact dimensions I'll post in a minute when I get home, but it has a heater, external filter, bubbler & a crappy led
light (hence no plants until I get a better one).