Looking for a good cost effective sub-substrate, the below image is holding approx 30 litre's of soil with 10 bags of 6"x 3" slate making a lot of soil. I have got 25kg of play sand but can't bag it as it is to fine, in turn, makes it useless for holding large stones in place as there is no friction. I have slate but that is probably too coarse for the main tank, I have read about cat litter (non-fragranced) and pea shingle in media bags can do the job.
So I'm wondering what others are using for building up their mounds/slopes?
So I'm wondering what others are using for building up their mounds/slopes?