ESV has trace minerals in it. If the tank is densely populated with corals I would recommend Tropic Marin A+K, but without regularly ICP testing I wouldn't get too deep into it. There's risk involved. The salifert potassium testlkit is in line with the ICP testing that ive done. Wouldn't bet bad to keep that kit and an additive handy. Tests for iodine, iron, manganese, zinc, fluoride, zinc etc... either don't exist or just suck to test and dose for manually.