I had to learn the hard way that a sump really is a necessity on a reef tank. On a FOWLR not so much.
Look at the link on my sig, it shows the progress of my years of tanks. I will say, that once I added a sump/refugium and got meticulous with doing 5G a DAY in water changes just to keep all the parameters stable my tank has been PERFECT in water quality. I am talking down to things like Silica, Strontium, Iodine, Magnesium, etc.
Just this month I spent another $600 on my tank. Replaced my skimmer for the 4th time to finally a Remora. Also changed out my 2x65w PC light for a 4x24w T5HO light and now I have 3x the PAR lighting.