Most modern salt mixes split into two categories. Reef-grade salts are formulated for stony coral systems and ship with elevated calcium (420-450 ppm), alkalinity (8-9 dKH), magnesium (1300-1450 ppm), and a full trace element profile. FOWLR (Fish Only With Live Rock) salts are simpler - lower calcium and alkalinity, no extra trace elements, designed for tanks where the focus is fish and live rock biology rather than coral growth. If you are running any stony coral, the reef-grade salt is mandatory; if you are running a FOWLR system, the FOWLR salt is cheaper and works fine.
Calcium and alkalinity are the two numbers that matter most for stony corals because both feed the calcification process. Calcium is the building block, alkalinity is the buffer that keeps pH stable while corals deposit skeleton. Magnesium is the supporting cast that keeps calcium and alkalinity from precipitating out of solution at high concentrations. The relationship is delicate - hit one too high and the others crash within hours. A good salt mix lands all three in the right ratio out of the box so a fresh water change does not throw your chemistry off.
Tropic Marin Pro Reef and Red Sea Coral Pro are the consistent reef-tank choices for SPS-dominant systems. Both deliver elevated parameters out of the box and have tight quality control batch-to-batch. Tropic Marin Pro Reef is famously consistent across every bucket; Red Sea Coral Pro is slightly higher in calcium and alkalinity, which suits high-demand SPS tanks. Instant Ocean Reef Crystals is the value choice and is fine for mixed-reef and FOWLR systems but runs slightly lower on alkalinity. Fritz RPM is gaining ground for its speed of dissolution and clean mix-up. For pure FOWLR setups, Instant Ocean (the original blue bag) remains the cheapest and most widely available option.
Salt should be mixed with RO/DI water (not tap, never tap), aerated for at least 6 hours, and brought to temperature and salinity before it touches your tank. Mixing into the display directly is a mistake hobbyists pay for in coral tissue recession and fish stress. Salinity targets: 1.025-1.026 specific gravity for reef tanks, 1.020-1.024 for FOWLR. Always confirm with a refractometer that you have calibrated to RO/DI zero - hydrometers and uncalibrated refractometers are the most common reason for "my parameters were perfect but everything died" stories.
Switching is a slow process. Do small water changes (5-10%) with the new brand for the first month while testing parameters before and after each change. If the new salt mixes to higher calcium or alkalinity than your tank currently holds, the bump will arrive in increments instead of all at once. Never switch in the middle of a coral health crisis - wait for stability, then switch, never the other way around. Most parameter swings during a brand switch are caused by the new salt simply being closer to its target than your old salt was.