Thanks for the replies everyone! I agree it is stocked to the max, if not, overstocked. I do 30-40 water changes every Friday without fail.
Regarding the denison barbs, they have yet to show any aggression towards each other/other fish, they group nicely, however it sounds like I should consider moving them to my other tank and increasing the numbers!
The congos are recent additions, and they are absolutely massive. I have owned them before but never seen them this fully grown before, so when I added them to the tank I was worried about everyone else’s space. Especially as I have nearly 50 other small tetras.
I will move the Denisons and am glad to hear everyone else seems like to will work