Is the filter in the photo the only one it may be possible that the water flow is not enough and did you start with all dry rock or some dry and some live? I have a 15 gallon tank that has manmade live rock two 30 gallon per hour hang on aqua clear filters and a power head with an adjustable pulse and flow rate.The light is an led system. What type of water do you mix your salt with? I use nature’s ocean sea water and change 2 gallons per week and do not use a protein skimmer or any type of filter material the only thing in the filters is ceramic tubes and a thin sand bed for the substrate and I have had good results.