Saltwater is the lifeblood of our marine aquariums and you need to remember that the salt in our oceans is a huge mix of different elements... not just your normal table salt!
With so many brands of salt out there it can be difficult to know which one to choose but we wholeheartedly recommend salts by Tropic Marin as it's the brand we, here at TMC, have chosen to use for nearly 50 years because we genuinely believe is the very best available. That said, making, measuring and using salt is the same process, no matter which brand you choose, so we hope the below information is useful!
Measuring Salt Content in water
To make salt up, we need to know how to measure the salt content in water. There are conductivity devices which will calculate the salinity of water which are expensive and not commonly used but the most common bits of kit which will essentially give us the same answer, are the hydrometer and the refractometer. There are two different measurements that can be used when testing saltwater: salinity (total salt content) or specific gravity (density of the water).
Specific Gravity is linked to temperature so you need to know what temperature your aquarium is versus the temperature that your hydrometer is calibrated or made to measure at. Most hydrometers come with a conversion chart for different temperatures.
Refractometers can usually compensate for temperature differences of up to 5oC from calibration and can give both salinity/specific gravity measurements. Hydrometers are simpler, and often cheaper, but usually only give specific gravity measurements at a pre-determined temperature. TMC/Tropic Marin® hydrometers are set to read specific gravity at 25°C, unlike nearly every other hydrometer on the market.
For a fish only tank, a specific gravity of 1.020 to 1.025 at 25°C is ideal, whilst corals and inverts prefer it higher at 1.024 to 1.027. In the oceans, there is an average concentration of 35g of salt for every litre of sea water. Due to crystallization water in the sea salt and the hygroscopic nature of salt (it will take moisture from the atmosphere) you may need more than 35g per litre of RO to make up your salt water. Tropic Marin salts are the driest brand out there giving the best yield ... handy when you're dealing with 100,000's of litres of saltwater a day like TMC!
TIP: Over time, water will evaporate from your tank, causing the salt level to slowly increase. Always use RO (Reverse Osmosis) water and not salt water to replace evaporated water.
Mixing Salt Water
Seawater contains more than just sodium chloride salt. If analysed, you will find most elements from the periodic table present. A quality, branded synthetic salt, such as REEF-Salt by Tropic Marin will contain all of the elements in just the right ratios - perfect for all marine aquariums, and your fish, corals and inverts will be maintained in optimum health.
When making a salt water mix, slowly add salt to water, not the other way around. You may wish to use rubber gloves as the mixture can be quite caustic before it fully dissolves and can make some people itchy. Never add powdered salt mix directly to an aquarium as it will be harmful to your aquarium inhabitants!
Testing the Water
To help maintain the perfect balance of elements as your fish and inverts grow, we recommend testing regularly for KH, calcium and magnesium, with Tropic Marin® test kits. This should be done alongside your regular testing routines of ammonia, nitrite, nitrate and phosphate.
Fish only, as well as soft and LPS coral tanks, can benefit from having Tropic Marin® ALL-FOR-REEF added, depending on KH level (test before adding). This will top up KH, calcium, magnesium and trace elements in line with the average consumption levels in the aquarium.
To help improve coral growth and reduce algae growth, we recommend regularly testing for nitrate (NO3) and phosphate (PO4), and use water changes and Tropic Marin Elimi-Phos or Bacto Pellets to help reduce high levels - optimum levels are 0.03ppm phosphate and 1-5ppm nitrate.
For a quick reference of what parameters should be what, see below!