Preparing sea water
The starting water which you use when preparing the sea water should be as pure as possible. Water from a reverse osmosis system or distilled water are best. You should use tap water only if it is guaranteed free of harmful substances (copper, nitrate, phosphate, etc.). The water should not be too cold when mixing. Around room temperature is ideal, in order to prevent subsequent lime deposits on the inside of the bucket. It is best to leave it overnight in a room at normal temperature.
40 g or 1 slightly heaped dosage-spoon of Nano Marinus Reef Salt to 1 litre of water produces an ideal density of approx. 1.023 (at 25 °C). The water can be used as soon as all salt constituents have dissolved and it is clear. The density should always be checked with the densimeter beforehand, however. If the density is too low, add a little salt. If the density is too high, add a little starting water.
Never pour sea salt directly into the aquarium!
Note on the required quantity
Sea water aquaria with a focus on fish are generally run with a density of 1.020-1.022, as a lower salt content results in less "osmotic stress" for the fish. The information on the pack for standard salts generally relates to the (lower) salt content required for this density level: 1 kg for 30 l of sea water.
Corals, crustaceans and other invertebrates feel more at home at slightly higher salt content levels, however. These conditions also offer a better supply of minerals (calcium, magnesium, etc.). As nano sea water aquaria are primarily suitable for keeping corals and invertebrates and less so for fish on account of their small size, Dennerle recommends an ideal density of 1.023. At this density, 1 kg of sea salt is sufficient for 25 l of sea water.
Sea salt is hygroscopic – it readily attracts moisture from the surrounding environment. It becomes lumpy as a result, or may even acquire liquid form when high humidity prevails. The bag should therefore always be closed airtight immediately after use. Clips such as are used to seal freezer bags are suitable for this purpose. A better and more reliable alternative is to keep sea salt in an airtight plastic box, however.