Mopani is not suitable for Panaques (royal plecs, blue eyes etc) to rasp on as it has been sand blasted leaving only parts that are indigestable, the plecs will rasp on and pass it but will gain no benefit from it resulting in small skinny looking unhealthy specimins. Royals should grow to around 12" within 10 years but very few do due to a lack of proper wood in their diet, when keeping these fish new pieces of wood should be added monthly as only the very top layers of wood contain the lignin which is essential for them to grow.