Fahaka not growing

[Indeed]

My fahaka won't grow or at least is growing around 10x slower than the rest of the lot he came with.

To start i do know how fast he has grown in comparison to the others that he came to the store with (the store i work at).
A friend of mine bought one and so did I. His is now 8-9" 8 months after purchase, mine is now only 3" his is in a 55g, mine is in a 120g.
He also feeds relatively the same food as me; krill, shrimp, scallops, snails, crayfish, and crab. I also feed about 2x his body weight a
day and he eats it all. I thought it might be a parasite so I've tried dossing prazi-pro for some time with no change in behavior or growth
rate, so i stopped dosing. I'm just out of ideas as to whats causing his lack of growth. I am about to say screw it and buy a 8" one I've
been eyeballing for a week now.

Any advice, suggestions?

*edit* the goldfish he is with that were originally for food (i was weening him off live food at the time) are now twice his size.
My puffer tolerates goldfish for some reason, i think he got tired of the taste. but how are they 2x bigger than him? my puffer eats tons
all the time and is very fat, just not big =/

[Terrance]

Weekly water change?
Does he look skinny?
Any stringy poop?
Feed him food soaked with prazipro.

[PolishPuff]

+1

Weekly water change?
Does he look skinny?
Any stringy poop?
Feed him food soaked with prazipro.

Hospital section

PLS answer ALL questions in red

[Indeed]

yes, i do once a week 10-20% water change, i also run a uv sterilizer to keep things extra clean.
I soaked his food in that stuff everyday for 3 days in addition to dosing the tank. He doesn't look
skinny at all. he is very rounded and full bodied, eats to the point of being super bulgy at least
2 times a day. haven't actually seen him poop, tank is heavily planted and he spends half his time
in the plants, guess thats why i haven't seen any waste.

the only thing i think may be a culprit is he was in a 10gal medical tank for 1 month when i first got him
(he was 1.5-2"). but i have never seen a fish get stunted that fast. So i am basically clueless and pulling
at straws... water tests all ready 0 with ph at 7.2 and a temp of 78-80F.

[Terrance]

Try 1-2 weeks of feeding prazipro. If that doesnt work, then get the jungle liquid med.

[puffykid]

yes, i do once a week 10-20% water change, i also run a uv sterilizer to keep things extra clean.
I soaked his food in that stuff everyday for 3 days in addition to dosing the tank. He doesn't look
skinny at all. he is very rounded and full bodied, eats to the point of being super bulgy at least
2 times a day. haven't actually seen him poop, tank is heavily planted and he spends half his time
in the plants, guess thats why i haven't seen any waste.

the only thing i think may be a culprit is he was in a 10gal medical tank for 1 month when i first got him
(he was 1.5-2"). but i have never seen a fish get stunted that fast. So i am basically clueless and pulling
at straws... water tests all ready 0 with ph at 7.2 and a temp of 78-80F.

I think that the time spent in the 10g did probably stunt him a bit, I know that seems ridiculous as that doesn't seem to be much time at all but this is a fish that is suppose to grow 1 inch per month minimum for the first year or so. Most people use medicine tanks in the 55g range for these guys. I am not trying to make you feel bad for your care of your fish, and he will still live a long and happy life if just smaller. Also I saw that you said he is in a planted tank, and so your nitrates are low I would still however suggest that you up the water changes up to about 35% a week. This way you remove more of the total dissolved solutes that are in the tank, and help replace more of the trace minerals that get depleted in your tank. Puffers are still wild caught, which means that they are originally from an open system of the stream or lake where they were born to the closed system of your tank. While we cannot hope to replicate the amount of water turn over that occurs in the rivers that they were born. Water changes help to keep the balance of other aspects of the tank that we can't measure.

Otherwise great job on being a good puffer parent and keeping your buddy in the correct tank size. This will help your puffer to have less problems down the road (meaning less medication and treatments for you) and to live a much happier life then your friends one in a 55g tank.