75 gallon cichlid stocking

Sounds great! Fully stocked is a word that means different things to people. After time I began to realize how much less livestock is really more enjoyment for all. Keep in mind that those severum will grow to possibly over 6 inches. The firemouth will probably get to that size too and my may encounter some territorial squabbles.

I don't know that adding a blue acara would be a problem but I would hesitate each time I add livestock. Those fish won't be babies eventually and they can all grow quite rapidly. It's not a matter of your filtration unit or water changes and more a matter of the livestock themselves, their comfort levels and behavior. Unless you know the behavior patterns of your fish, you won't be able to determine how the impact of adding other semi-aggressive or aggressive livestock are impacting them.

Right now you've got 10 fish in the tank - and they are at their smallest sizes. I dislike the 1 gallon per fish rule because it really doesn't take into account many variables. Consider the activity level of your fish and their swimming habits, which means a good amount of being near each other. There is also an unpredictability factor of now knowing how all your fish will react. I find that when there is more space, my fish are more interesting to watch.

So all I can say is that, for now, it might not add so much of a problem but it's something you'll need to keep an eye on going forward. Cichlids are a lot of fun. Would love to see your tank. I'll be posting some new photos here.