I'm planning a low maintenance tank and was thinking of compost under sand, then someone mentioned this product with some nutritional content. Does anyone know if it's sharp and angular? There will be cories in the tank so I need it to be safe for them. None of the pictures online are detailed enough to see. I have found a thread on another forum with good pics of the regular fluorite, but not the sand. Even the high res image from seachem isn't close up enough. Thanks for any tips.