Anytime you have a tank of Malawi fish, and when you come to the glass, and they don't meet you there wagging their tails off, something is not right. You might want to look at your set up and try to figure out what the cause may be. It could be the tankmates, not picking the right ones can effect your tank. So we need to ID your fish. Where is your tank located? Is it in a quite area or a busy area. How often do you clean your tank, and what percentage of water do you change? Need your Temperature, pH, and what and how often you feed. What kind of filtration?
When you do a water change, just wipe down the glass too, and then you don't need an algae eater. If Algae is taking over your tank, then you might be feeding too much food, not enough water changes, or leaving your light on too long. Many fish from Malawi love to graze on algae, so it is a good thing as long as it is green.
You'll have to start a new question, with your reply, just label it #2. Usually thru the process of elimination you can figure it all out.