Nice, Ghost Knives are a lot of fun to watch at night. Make sure you have dim LED or night light of some kind to you can see them swim in the dark. That is about the only time I see mine or just a little after feeding time he pops his head out to grab a mouth full. Last I was able to measure mine he was upwards of 18 inches. I haven't gotten a chance to measure in a about a year and half so possibly a little bigger now. I have 4" pvc pipe covered in slate in my tank so he can hid and fit. I used have 3 inch pipe but he got to tall for it so I had to change it all out.