I've had my jardini since January at 3". He's around 8" now. Growth has slowed down since he stopped eating pellets but I gave in and have been feeding him shrimp the last month to bulk up.
He looks like a nice fish supervee try stuffing pellets in the shrimp so at least he doesn't go off the taste all together , what's your wc schedule ? That plays a big part in growth IMO balanced water stops stunting