20 gallon shallow reef tank

2 1/2 feet wide, 10in tall, 17 deep, with an external overflow box built into the tank and a 20 gallon long sump. return pump 500gph, 300gph pump for the water fall, two nano is behind the rock pile, phosban 150 reactor with bio pellets, 150w metal halide 14k bulb with blue t5 as compliments, sock for the filter, and a chiller heater set up. system is being dosed with the kalkwasser method using a aqualifter pump to top off water. once a week i use half teaspoon of purple up and a squirt of b