I currently have 2 cichlids (a melanochromis auratus and a labidochromis freibergi). This was a tank with multiple types of animals, but I am changing it to be just for cichlids now that these two have grown some and need more space. It is a 20 long with a good filter and LOTS of decor to hide in (caves, plants, logs, etc). How many cichlids can I get? I have read that overstocking reduces territorial aggression. Are there good types to put with these two? Thank you!