I'm new to NPTs, having just read and loved Ecology of the Planted Aquarium. The description of the aquarist who fails with plants and ends up discouraged before going 'high tech' really resonated with me! I'm keen to convert my four footer to an NPT, mainly to conserve water with fewer changes, but before I do so, I have a few questions.
This is going to sound dumb, but can someone describe to me what "potting soil" is like? Where I'm from we don't have "potting soil" per se, it's called "potting mix" and it does not contain any real soil - it is a mixture of partly-composted bark and a little bit of river sand. Would this be suitable? Most potting mixes also contain a lot of water-holding crystals since we are constantly in drought.
I've tried submerging garden soil in a bucket, to see what would happen, and ended up with an oil slick on the water surface. The slick is presumably from gum tree (eucalypt) oils - that's what it smells like, at any rate. Gum trees are poisonous, so I don't think that this would be safe even if I can get rid of the oil somehow.
I keep male fancy guppies in a show tank and some of the strains are weak, overbred little things. Are they likely to fall apart if I put them into an NPT?
Any ideas, thoughts, suggestions would be much appreciated.