Hey I suggest sticking to one thread since we're pretty much discussing the same thing on your two threads
Knowing now that your tank has a 6 foot length your suggested stocking might possibly work, especially due to the peaceful nature of the severum and the oscar but you need to be ready to give up one of your large cichlids if they don't get along. The green terror is a beauty though!
So yeah I'd suggest 3 cichlids only but its your tank if you wanna go for 4 why not! Just take the following steps to maximize your chances of success.
1. Start them out young as possible and put them in at the same time. This will give them a chance to get used to each other, and wont drop a new fish into an already established pecking order.
2. Provide lots and lots of hiding places such as caves, over hangs, using driftwood, plants, pots and rocks. They need to be able to get out of sight of each other. An angry cichlid will chase another literally to the death if it feels like it. The Dempsey will be the smallest so make caves only he can fit in. Do this for the next smallest fish and the third smallest fish. The idea is giving them a place where the largest fish cant reach them. Even if one of the smaller fish turns out to be a bully, a cave is easier for a fish to defend than fighting in open water.
3. Provide dither fish. A dither fish is a fast, tough fish that the cichlids can take their aggression out on. For example if one is angry that he couldn't beat on an other, he'll chase the dither fish instead. Hence tough and fast. Large silver dollars are perfect dither fish for this tank.
4. Feed them a lot! Lots of fights will break out concerning food. Feed at opposite ends of the tank at the same time, and make sure that each fish gets enough to eat that he wont have to worry about competing for food. This is the one time overfeeding is ok ,and please monitor your nitrate levels.
5. Try to get all male fish as females can be more territorial. Also you don't want a hybrid pair forming up and with the Dempsey, terror and Oscar this is a possibility. Hybrids are generally frowned upon, and if you get a breeding pair in that tank, say goodbye to all your other fish. Males tend to look better too
6. Keep the temperature as low as you possibly can while staying within their suggested range. Its been shown that higher temps can lead to higher aggression levels in large cichlids.
7. Lastly, watch your fish a lot! Be on a constant lookout for torn fins, wounds, fights, and react accordingly. The Dempsey and the terror will be the most aggressive and will need the most monitoring.
Good luck and keep us posted !
So yeah I'd suggest 3 cichlids only but its your tank if you wanna go for 4 why not! Just take the following steps to maximize your chances of success.
1. Start them out young as possible and put them in at the same time. This will give them a chance to get used to each other, and wont drop a new fish into an already established pecking order.
2. Provide lots and lots of hiding places such as caves, over hangs, using driftwood, plants, pots and rocks. They need to be able to get out of sight of each other. An angry cichlid will chase another literally to the death if it feels like it. The Dempsey will be the smallest so make caves only he can fit in. Do this for the next smallest fish and the third smallest fish. The idea is giving them a place where the largest fish cant reach them. Even if one of the smaller fish turns out to be a bully, a cave is easier for a fish to defend than fighting in open water.
3. Provide dither fish. A dither fish is a fast, tough fish that the cichlids can take their aggression out on. For example if one is angry that he couldn't beat on an other, he'll chase the dither fish instead. Hence tough and fast. Large silver dollars are perfect dither fish for this tank.
4. Feed them a lot! Lots of fights will break out concerning food. Feed at opposite ends of the tank at the same time, and make sure that each fish gets enough to eat that he wont have to worry about competing for food. This is the one time overfeeding is ok ,and please monitor your nitrate levels.
5. Try to get all male fish as females can be more territorial. Also you don't want a hybrid pair forming up and with the Dempsey, terror and Oscar this is a possibility. Hybrids are generally frowned upon, and if you get a breeding pair in that tank, say goodbye to all your other fish. Males tend to look better too
6. Keep the temperature as low as you possibly can while staying within their suggested range. Its been shown that higher temps can lead to higher aggression levels in large cichlids.
7. Lastly, watch your fish a lot! Be on a constant lookout for torn fins, wounds, fights, and react accordingly. The Dempsey and the terror will be the most aggressive and will need the most monitoring.
Good luck and keep us posted !
thankyou. im going to have to sit and plan the lay out of the tank very carefully, so i can give this the best chance of working 
