Cichlids have a reputation for being aggressive and territorial, difficult fish to put into a community tank. Companion fish need to be carefully chosen for temperament and an ability to defend themselves. Algae eaters have a reputation as placid, easily intimidated creatures, but are popular with aquarium owners trying to keep their maintenance time down.
Cichlids Eat Snails
A variety of snails exist that love eating algae. They can do a good job of keeping the glass clean, and are very low maintenance. Unfortunately, cichlids eat snails. If you have a snail infestation, a few cichlids can be an answer, but if your snails were put there with a purpose in mind, such as keeping the tank clean, they are likely to become fish food.
Catfish are Cleaners
Some species of catfish can live in a tank with cichlids. Both the hop lo and the pictus catfish are known to survive the experience. But catfish tend to be bottom feeders, not glass cleaning algae eaters. Aquarium owners buy them in the hope that they'll do some housekeeping, but end up disappointed, and still scraping the glass.
Chinese Algae Eaters are Territorial
Chinese algae eaters will certainly devour a lot of the green film you want to get rid of. They are also known to survive in cichlid tanks. However, when they grow to full size, they can become quite territorial and will aggressively attack any other fish that comes too close. As cichlids tend to the same behaviour, this can create a situation where fish can be injured or killed.
Plecos Can Survive
Plecos are algae eaters. But most plecos are problems waiting to happen in an aquarium: They grow too big, and they create a lot of waste. When they get too big, they tend to eat less algae and start cleaning up old food or snacking on your other fish. In addition, cichlids have an unpleasant habit of eating out plecos' eyes. However, the bristlenose pleco doesn't get too big, eats algae voraciously, and is well armed to protect itself from attack.
Size matters; buying a larger companion fish to start with will help ensure the addition's survival. Cichlids like higher pH levels, 8 and above, so it's important to note what the additional species will tolerate as well. And with any territorial fish, overcrowding should be avoided, to prevent battles for limited space.