Aquarium Salt Mix Calculator — Marine & Freshwater

Aquarium Salt Guide

What do I need to know about Marine Salinity Standards?

Reef aquariums: 35 ppt (parts per thousand) = specific gravity 1.025 at 25°C. This matches natural ocean water. Coral and invertebrates thrive at this level. Fish-only marine: 30-32 ppt (SG 1.020-1.022). Slightly lower than natural ocean — reduces parasite reproduction rates. Salt cost savings. Hyposalinity treatment: 14 ppt (SG 1.009-1.010). Therapeutic level — eliminates marine ich (Cryptocaryon irritans) without harming fish. Must be maintained for 6-8 weeks minimum. Not suitable with invertebrates present, since the treatment level of salinity used to eliminate ich is toxic to shrimp, snails, and other invertebrates in the same tank.

What do I need to know about Mixing Marine Salt Correctly?

Use RO/DI water — never tap water. Tap water contains chlorine, copper, nitrates, phosphates. Heat water to 25°C before adding salt. Add salt slowly to water (never water to salt). Mix vigorously with a powerhead or large stir paddle for 12-24 hours. Aerate to drive off CO2 — raises pH. Check salinity after 24 hours with refractometer (NOT a hydrometer — refractometers are far more accurate). Refractometer calibration: zero with RO water, check with calibration fluid (53ppt) periodically. Inaccurate hydrometers are a common source of stocking and dosing errors, which is why serious reef keepers invest in a proper refractometer instead.

What should I know about Water Changes?

Standard reef tank: 10-20% weekly water change. Removes accumulated nitrates, phosphates, replenishes trace elements depleted by corals. New water must match tank: same salinity, similar temperature (±1°C), pH within 0.2. Premixed water in a separate brute can with powerhead — mix 24 hours before use. Acclimating fish to new salinity: never change more than 0.001 SG per hour. Faster changes cause osmotic shock and fish death. Drip acclimation: tube from tank to bag with an airline valve regulated to a slow drip, gradually mixing tank water into the transport bag over 30-60 minutes to acclimate new fish safely.

What's the key thing to understand about Freshwater Salt — Therapeutic?

Aquarium salt (sodium chloride only — NOT marine salt) used therapeutically in freshwater. Doses: low dose: 1g/litre. Useful for ich treatment, slime coat support, mild bacterial infections. Most fish tolerate this indefinitely. Medium dose: 2g/litre. More aggressive ich treatment. Many species (livebearers, cichlids) tolerate. Catfish, scaleless species, plants suffer. High dose: 3g/litre. Strong treatment but limited duration (10-14 days). Many sensitive species cannot tolerate. CAUTION: salt does not evaporate with water changes, so repeated partial water changes without accounting for this will gradually concentrate salt to dangerous levels if not carefully tracked.