The bucket version of this product has now been discontinued and is only available in a boxed version containing sealed bags of salt inside. Seachem Reef Salt is a chemically sound blend of salts designed to replicate natural reef waters. It is ideal for both reef aquaria and fish only aquaria. It is specifically formulated to maintain ideal and stable seawater concentrations of magnesium, calcium, and strontium with adequate alkalinity and pH for closed aquarium systems. It contains all essential major, minor, and trace components found in natural reef waters, but contains no detectable quantities of toxic or non-essential components such as nitrate, phosphate, silicate, arsenic, cadmium, or beryllium. Biological components, such as vitamins and amino acids, are unstable in concentrated salt. Since they are depleted from the aquarium more rapidly than they can be replenished by routine water changes, these components are best supplied by regular addition of Seachem\'s Reef Plus. Reef Salt mixes with excellent clarity to a pH of 8.2-8.4, an alkalinity of 4 meq/L and calcium of 400-420 mg/L, depending on specific gravity. DIRECTIONS: Each 7.8 kg (17.2 lbs), when added to 200 Litres (50 gallons) will prepare 200 Litres of seawater at a specific gravity of 1.022. One cup of salt (about 225 g) will prepare approximately 1.5 gallons. Mix thoroughly until dissolved. Check specific gravity with a hydrometer and adjust to desired level. For reef aquaria, 1.022 is recommended; for fish only aquaria, 1.018-1.020 works well. pH should be between 8.2-8.4. Alkalinity should be about 4.0-5.0 meq/L, depending on specific gravity. Calcium concentration should be between 380-430 mg/L, depending on specific gravity. In reef aquaria, use Seachem\'s Reef Complete and Reef Calcium to restore any depletion of calcium between water changes. Use Marine Buffer to restore pH or Reef Builder to restore alkalinity. Exceeding 430 mg/L calcium is not recommended, since concentrations in excess of 400 mg/L serve no useful purpose and can adversely disrupt alkalinity and pH. In fish only aquaria, calcium concentrations are not critical and calcium supplementation serves no purpose. This particular product is supplied in a box rather than a resealable tub which provides better value. The box is broken down into several sealed bags preventing the salt from getting exposed to air once the box is open.