Give us a full tank shot, post parameters too, can U give us full specs ?
Protein skimmer ? RODI
water ? Sump ? Powerheads ? HOB
filters ? Temp ? Mg
? PH in the morning vs in the evening? Brand of salt you're using? Lighting system ? T8, T5, T5HO, LEDs? Wattage ? Color of bulbs ? Live sand substrate or not ? Total pounds of Live rock and base rock ?
Also what's your stocking ? And maintenance schedule ? Any algae problems ?
I started like U with my 20g. Two clownfish, a protein skimmer, few easy corals but a powerfull lighting system.
On the picture your tank seems to run only actinic lighting, but the corals seems healty. And the ocellaris clown on the picture seems healty and free of diseases.