The common problem with FO
tanks is probably overstocking and under filtration. Tanks that are FOWLR
or reef have a tremendious amount of surface area for biological filtration because of the sand bed and the surface area on and in the live rocks.
Fish Only setups often are overcrowded putting an even greater load on the biological filtration system. Adding a sand bed will increase the surface area for the bactera to populate and even though reefers might say that wet/drys are bad they really can be of great benifit for a fish only setup because the bioball chamber is an excellent ammonia and nitrite removal facility.
Even fish only systems will benifit from the use of a skimmer and regular water changes.