I have been wondering about alternative substrate sources (never even considered poo), specifically mixing sources that could eliminate or reduce the need for chemical fertilizer additives.
The benefits of dirt, peat, sand, dry leaves/compost etc. is undeniable when carried out properly. I have found this is still lacking iron and possibly other trace nutrients. Safe poo does fit the void (I'd cook it longer), but I don't have a dog (lol) and don't trust someone else's judgement of the safety of their dog's poo. Cat poo is not appropriate. I have been considering sources such as beans, nuts (be careful), seeds, etc. Feeding live, high protein foods (eg mice) is always a great source of iron, but my lil fishies won't be feeding on that.
Any wisdom you could share for considering non poo alternatives to the substrate?