I have 6 clown loaches in a 410 gallon aquarium. They have been in there for at least 2 years. They were pretty small (1.5 inches) when I got them but they are only about 4 inches now and pretty uniform in size. They get flake food every day and frozen food every other day, a variety of types of each. They have always had nice rounded bodies and are voracious eaters of all foods. The pH is 6.8, temperature 79 degrees fahrenheit, and continuous water change of about 30 gallons per day. There are lots of places where my catfish and plecostomous hide but the clowns never do. They also never lay on their sides.The tank is crowded with plants which, I suppose helps them be comfortable.
I don't really know why they aren't growing more quickly but I'm not concerned about it because they sure seem healthy and happy. It would be interesting to find out why there are such disparate experiences regarding growth rate. My aquarium is certainly large enough. The filtration is good at about 2800 gallons per hour through a wet/dry filter. There are no aggression problems. As I said, the tank is heavily planted and there is a lot of pearling going on. I have even had to alter my cover so that one of my lilies has room above the water for the flowers it keeps putting out - about 18 in the last 6 months!
Love this hobby!