art_b

Sorry for asking something that other people might consider a stupid question. This has confused me for quite some time . My tank size in cm is 90x45x45 which equates to 182 liters. However, in terms of water volume, it could well be around 160 liters or less considering the displacement cause by the substrate, plants, and other decorations in the tank.

In your dosing instructions, for example on Flourish, it says "Use 1 capful (5 mL) for each 250 L (60 gallons) once or twice a week."

Am I suppose to dose for 182 litres (~3.5 ml), or only for the water volume of 160 liters (~3 ml) ?

Seachem

Typically, when supplementing you dose for the actual volume of water rather than the tank size.