HGF
Which is the optimal water level in the tank?
You should check that the water level is always between the minimum and the maximum level, both shown in the front of BLUWAVE filter. When you see that the water level in the tank is near to the minimum level, 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.