Agreed, was just an absolute minimum, but in reality 6 is ok as they don't get much more then 12" long. But sand beds that deep carry risks, especially when mixed with fish (or in this case eels) that disrupt and move the sand, exposing anaerobic bacteria in the lower sand layers to oxygen can cause die offs, resulting in major parameter swings. I personally never include anything larger then 1" that moves through/moves around sand for that reason. I prefer my sand sifters to be micro inverts/worms/micro stars6 inches? I think that's too shallow...
Big als in Calgary and Pisces, in fact I`ve seen them in many stores here at different times of the year. Canada is a big placeI haven't seen a Canadian location that has them, they are also know an Garden eels, Taenioconger hassi. you also need ALOT of sand bed, like 6 inches deep minimum. and I'm not sure how well they do on pellet food, from what I hear they need live.