From your first post I am guessing that the butterfly and wrasse are keeping the copepod population very low,which means that a member of the dragonet family will have a difficult time finding sufficient food to sustain itself. You had better hope that you can quickly convert your fish to prepared food. Don't count brine shrimp as food, nutritionally it is like cotton candy for fish. Best would be prawn ova, which you can get frozen. I am also concerned that this fish seems to mostly come from the Philippines, where cyanide is commonly used for capture, meaning that the animals will be short-lived. So...if you do get this fish you have a challenge ahead of you. But - it is gorgeous, I do see why you would want one. And yes, a 7 gallon qt would be sufficient for this fish, especially if you remove the sand.