Little baby Fahaka just not growing

I bought a Fahaka through Fosters and Smith a few months ago. Came in at just about 3 inches, hes still right around 3 inches, maybe gained a half an inch in about 4 months. Not at all what I was expecting. He was in a 75 gallon, super overfiltered tank, getting fed twice a day, sometimes once when he still looked full, skipping a day now and then when I either didnt get a chance to get home, or he was asleep when I got home late. He is now in a 120 gallon, and still same size. Should I expect him to grow a lot more, should I feed him maybe twice a day every day or 3 times a day? Just not sure why he hasnt shot up in size. Figured Id atleast have a 6 inch puffer at this point. He looks so cute all tiny in his huge tank, but realistically Id much rather him be up and healthy and growing. I wonder if he was in a tiny storage tank for so long at the hatchery or whatever that hes stunted? Anyone have any ideas? Oh and yes, water parameters are correct, and he has had a varied diet of shrimp, crab, crawfish, worms, and random tiny fish he picks out of his tank now and then.

Copied straight out of the pufferpedia...

Max. Size: 18 inches (43 cm) - Grows very fast, expect to grow an inch a month for their first year.

So being that he was three inches, I figured after 4 months another 3 inches wouldnt be hard to expect. figured AT LEAST 5inches, to a max of 7 at this point in time. Pufferpedia a little quick in there growth rate assumption?

I don't think So. I mean, he never gets awkwardly skinny between feedings, and always has a nice plump belly for quite awhile after being fed. Maybe I should throw some meds in the tank just to be sure? Can I treat ips in the 120 without messing up the other little fish swimming in there or should he be quarantined to medicate? I highly doubt that's the issue though, he seems to have a nice healthy shape to him. Ill see if I can manage to snag a few pics of him before and after feeding this evening.

Well, its been almost another 3 months. Still a healthy round little fellow. Definitely no IPs. Water parameters are perfect. Feeding clams, squid, redworms, and bloodworms for snacks. Fed once or twice a day depending on the shape of his belly. Perfectly active and happy, chases me around the tank especially when he sees his feeding cup. No growth though. Maybe he has gotten a little thicker, but Id say hes still right at or less than 4 inches. Anybody have any thoughts? I love this fish to death, but I got him this huge tank to make him happy and so I could have a monster grow up inside. Having a tiny little guy in this big 120 just seems like exactly the opposite of what I wanted lol. Luckily, I have been having more fun with my plant growth, so the tank at least looks great. Still really wish this guy would pack on some size. I even debated trading him for one that would actually grow, just would be sad to let go of my little wet pet.

Here we go. Couple shots of my little fella, and a shot of his healthy home. Excuse the bit of algae, just started using firts and Im getting the balance down. Tomorrow is algae killing day. Tank parameters are all still good. One fluval fx5 and one fluval 405. Hydor inline heater with the tank set at 79*F. And like I said above, red worms, clams, shrimp, squid, and bloodworms are all part of the diet. Feeding once or twice a day depending on his tummy size.