What do all of these have in common? They're all potential products of irregular or inconsistent cleaning. If you have a power filter (HOB, canister, internal), clean the pumphead, impeller, and other components regularly. Clean your filter hoses too. Make regular cleaning of all components of your tank a part of your routine. But don't stop there. Keep your supplies clean as well - buckets, water change hoses, brushes, etc.
Regular cleaning (in conjunction with water changes) will also result in healthier fish over time. Adopt a consistent cleaning routine and you'll spend less time problem solving. It's really that simple.
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub