PUF
Which is the optimal level of water in the tank?
You should check that the water is always between the minimum and the maximum level, both shnown in the front of BLUWAVE filter and in the tank. When you see that the water level in the tank is near to the minimum, add demineralised water (both in marine and freshwater aquarium) to replace which is lost by evaporation.
In any case, replace 5-10% of the water with demineralised water at least monthly.