There are many kinds of filtration, but not all are possible for cichlids.
Cichlids usually make very much dirt and the filter has to work very well.
You really should use a mechanical filter, not a biological, because biological are usually not strong enough. One of the best kinds of filtration for cichlids, but also expensive. But it's probably nothing for a 20-30 gallon tank. Air is enough for small breeding tanks at a size of 20-40 gallons or similar. If the tank is bigger you should use a powerhead.