Also it's a bad idea to mix and match rift lake cichlids and south/central american species. They have completely different water and habitat requirements. The two cichlid species you picked there may be compatible (i don't know much about africans), but the serpae tetras would not be. Most SA/CA (central/south american) species require soft acidic water (ph < 7.0). Especially tetras. Most rift lake cichlids requre hard alkaline water (ph > 7.0 usually 8+). This means that for a rift lake tank you are going to want to use buffers in the tank such as limestone, crushed coral etc to keep the ph up. This elevated ph will kill most acidic water species like tetras. ALso the rift lakes are really rocky and you need lots of rocks in a RL tank. On the other hand SA/CA species need water that is usually softer and more acidic than most tap water in the USA. This means that you will need to use plants, drfitwood, and non buffering rocks in your setup to try and get the ph down.