hello, I'm new to this forum, but I have been keeping cichlids from central and south america for a while, so I can help with a few suggestions if you want some super intelligent fish.
All of the ones I suggest have amazing coloration and are aggressive. They can usually be trained to accept food from your hand (careful your fingers!) and some even allow petting. Heavy filtration for all, and rocks, caves, and territories are a must. Here are some long-term ideas:
With a 75 gallon, you do have a few options.
Option 1: If you're looking to keep maybe one or two large cichlids (heavy filtration and heavy PWC's are a must) then you can long term house a jaguar cichlid and a salvini cichlid. The jaguar is considered one of the most aggressive and most intelligent cichlids available (some say it's even smarter than the oscar). Male Jaguars grow to about 14 inches and females around 10. The salvini cichlid only grows to around 7 inches, but no worries. That salvini can certainly handle a jaguar twice it's size because it is also of the same aggression level as the jaguar. The salvini is a bit shyer, but keep the lighting dim, and it shouldn't be too bad. Most likely, only fake plants can be kept, and they will be uprooted.
Option 2: You could also do two oscars. Each grow to about 13 inches. Gender and coloration do not matter so much. No plants. Very very heavy filtration to prevent hole in the head disease.
Option 3: One jack dempsey cichlid and a green terror cichlid. You could try a school of 8 tiger barbs as dithers, but don't be surprised if they eventually get eaten. It would be better if you added everyone while they are babies and allow them to all grow up together.
Option 4: A convict cichlid (females have better coloration, but males have that gorgeous nuchal hump), and a texas cichlid.
Option 5: One midas cichlid. Should be kept alone. If you like hybrids, then you can substitute for the Flowerhorn cichlid. Nothing else goes in with a single specimen, except for rock decorations and fake plants if you want some green.
Option 6: (a little bit of a different suggestion) You can go with a community with a lot of caution and monitoring. Cichlids vary personality from individual to individual (one green terror might be a monster when the next might be a wuss). TENTATIVELY and TECHNICALLY, you could keep ONE of the 10-12 inch cichlids mentioned above (texas, green terror, jack dempsey, oscar) with a school of 8 tiger barbs, and ONE convict cichlid. This is a very heavy load, so don't even try it unless you are willing to perform weekly 40% water changes and have your filtration with a more than adequate canister filter, and a more than adequate HOB filter for surface agitation. Ensure plenty of fake bushy plants for the barbs and rock caves/territories for the two cichlids. The tiger barbs should be added first and grow out to almost adult size then there are still no guarantees they will survive long term, but for the first couple of years they will be a joy to have. This suggestion is not suggested for the beginner because of the load, but if you are willing to handle the maintenance, then it can work.
Sorry for the long post, but examples/scenarios have always been extremely helpful to me in the past when it came time to plan. Cichlids are an absolute joy to keep. They will recognize and greet you when you approach the tank, they can be trained very easily, most are hardy and accept a wide variety of foods, and all are extremely intelligent. They like to pick up a piece of gravel in their mouth and place it elsewhere to their liking, or if you have a sand substrate, they will sift it through their gills (they do like to dig, so a sturdy rock structure may need to be siliconed together). Also, cichlids are one of those subjects that everyone tends to have different ideas on, so another person may come up right behind me and say that this is all trash. I don't ever suggest plecos because of the amount of waste they cause, and I am a diehard fan of ammonia fishless cycling because it's much cleaner than having something 'rotting' in your tank. And yes, your BGK will grow too large too quickly to keep in a 75 gallon. I'm just giving examples from knowledge I have gained in experience, research, and others' wise advice.
I hope this helps you. If not, then I hope it helps anyone looking towards cichlids.
