What is Salinity?

Salinity is the measure of how salty your water is. We test this using a refractometer, and want to aim for a salinity of 34ppm. We keep this stable by using an auto top up - which means as water evaporates from your tank, it is replaced periodically with RO water. We don’t use salt water to top up, as when water evaporates, it leaves the salt behind.

If your KH, Calcium, and Magnesium levels are high, it’s always worth checking your salinity, as these are at higher levels in saltier water.

How can it change?

Your salinity can only decrease if you remove saltwater, and replace some or all of it with RO water. If your salinity is ever too low, it’s important to bring it back up gradually, so try and do this over a number of days. The easiest way to do this is to put saltwater in your top up reservoir.

Your salinity can increase if you are dosing some types of product which buffer pH, or if you do a water change with water which has too high a salinity. If your salinity is ever too high, do small water changes (around 1L per 100L of tank water) per day until your salinity reading is right again.