I had 3 Black Ghost to start with. They were about 2 inch then. I had them in a 67G with 10 Clown Loach, 4 Black Widow Terta, 5 Rams, 2 plecos, 4 Mollies and 4 Swordtails. The Black Ghost grew fast, in about 2 months, one grow to about 5 inches, one to about 4, but the 3rd one still at aound 3 or less, but died later. They would swim around the tank,day or night, especially when I feed them with Blood Worms.
One fine day, my aunt brought me about 50 Gouramis, 10 plecos, and about 30 Swordtail and Platies from a friend who has a fish farm. Well, the tank was damm crowded. So I ordered a 180G. Now the tank is kind of empty. I have added 5 Redtail Sharks. A few of the Clown Loache died, I bought another 4 to replace them. The gourami and swordtails also died quite a few, now left with less than 20.
I was eager to get a Clown Knife ( 6 inches), and finally did. I had it in the 67G with a Dragon fish(6 inches) and a Flower Horn( also around 6inches). They seems to get along well.