hi, i read your article on terrariums.. v interesting.. and i have an ongoing problem with mould forming on top of the soil.(not only with contained plants, also with my potted plants. strangely, the plants are healthy (seemingly).i'm new to plants and have no idea why this happens! should i completely re pot all affected plants following advice given by you regarding gravel, sand and moss? thanks to anyone who can help! dalriana.