Saltwater Aquarium Charts, Tables and Quick Reference Numbers Worth Keeping Handy

In this guide

Marine fishkeeping involves more numbers than most freshwater setups, salinity, alkalinity, calcium and magnesium alongside the familiar ammonia, nitrite, nitrate and pH. Keeping a simple reference sheet near the tank, or saved on your phone, saves a lot of second guessing during routine testing.

Core Water Parameters for a Fish Only or Reef Tank

• Temperature: 24 to 27 degrees Celsius for most tropical marine fish and corals
• Salinity: 1.020 to 1.025 specific gravity for fish only tanks, 1.024 to 1.026 for reef tanks with corals
• pH: 8.1 to 8.4
• Ammonia and nitrite: zero, always, in an established tank
• Nitrate: below 20 parts per million for fish only tanks, generally below 10 parts per million for reef tanks with sensitive corals

Reef Tank Specific Parameters

• Calcium: 400 to 450 parts per million
• Alkalinity: 8 to 12 dKH
• Magnesium: 1250 to 1350 parts per million
• Phosphate: below 0.03 parts per million for tanks with stony corals, somewhat higher tolerances for soft coral or fish only setups

Useful Conversions

• 1 US gallon is approximately 3.785 litres
• 1 inch is approximately 2.54 centimetres
• 1 litre of seawater weighs approximately 1.025 kilograms, slightly more than plain freshwater due to dissolved salts
• Specific gravity of 1.025 corresponds to roughly 35 parts per thousand salinity, close to natural seawater

A Simple Stocking Guideline

The old rule of one inch of fish per gallon, or roughly one centimetre per four litres, is a very rough starting point at best for freshwater fish and is generally considered too generous for marine fish, which typically need more swimming room and produce more waste per centimetre of body length than most freshwater species. Marine stocking is better judged by researching each species individually and by adding fish gradually while monitoring nitrate over time, rather than relying on a single formula.

Feeding and Turnover Reference

• Filter or pump turnover for a fish only marine tank: roughly 5 to 10 times the tank volume per hour
• Filter or pump turnover for a reef tank: often 10 to 20 times the tank volume per hour once powerheads are included, since corals need considerably more flow than fish alone

None of these numbers are absolute rules. They are reasonable starting ranges drawn from widely used aquarium references, worth adjusting as you get to know your own tank's particular quirks and the specific species you keep.

Test Kits Available in India

Widely used marine test kit brands such as API, Salifert and Red Sea are all available to Indian hobbyists through online aquarium retailers, though import lead times mean it is worth ordering refills before you actually run out, rather than waiting until a kit is empty. Digital handheld testers for salinity and pH are also increasingly common and can save time on routine testing once you have cross checked one against a reliable kit.

Article content © S Vejay Anand. All rights reserved.