How much Zelbrite do I need in my filter?
Zelbrite has a lower bulk density than sand, hence you require 75% by weight of the amount of sand required, and this will vary depending on the size of the filter. A 15kg bag of Zelbrite is equivalent in volume to a 20kg bag of sand. Most filters have a name plate which will give you the size of the tank, e.g. 24in and also specify the amount of sand required, for example 140kg, which is 7x20kg bags of sand, or 7x15kg bags of Zelbrite.
