Calculator
Reef Salt Cost Calculator
A cheaper box isn't a cheaper salt. What matters is cost per mixed gallon — and what your water changes actually cost you each month. Here's both, ranked.
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Why cost per gallon, not per box
Salt is sold by the box, but you use it by the gallon. Two boxes at the same price can make very different amounts of saltwater, so the only fair comparison is price ÷ gallons the box actually mixes (at reef salinity, ~1.025). That's what we rank on here.
Your real monthly cost
Salt is the quiet recurring expense of the hobby. Your monthly cost is simply your tank volume × your water-change percentage × how often you change — times the cost per gallon of your salt. A 75-gallon tank doing weekly 10% changes goes through about 32 gallons of new saltwater a month; the salt you pick decides whether that's $10 or $25.
Cheap salt vs. reef salt
Base salts (like plain Instant Ocean) mix to near-natural-seawater levels and cost the least — great for fish-only tanks and fine for many mixed reefs that dose separately. "Reef" and "Pro" salts run elevated alkalinity, calcium, and magnesium to feed coral growth, at a higher price per gallon. For an SPS-heavy tank the elevated salt can be worth it; for softies and LPS, the cheaper salt usually is.
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