I change about 80% every 6 days. If I wait 7 days the nitrates are red. I use a few different pellets (Omega One, NLS), Ken's freeze-dried krill superba, and the occasional earthworm.
He grows so slowly I hardly notice the trailers. They've become distinct in the past two years or so.
I think FMs are a type of eartheater(?) so I should have sand instead of gravel. He doesn't seem to mind. In the future I'd like to do a thorichthys tank, with some of his less famous kin: http://www.fishbase.org/identification/SpeciesList.php?genus=Thorichthys
Filament Barbs would make for a great tank all by themselves. They make chirping sounds when they chase each other. There's so many barbs that you rarely see in the hobby: http://www.seriouslyfish.com/group/barbs-relatives/
I see. Looks like I have another 18 months or so with mine then. I've had him for just over 18 months, and he's started to develop a extended dorsal fin. Definitely right though. I remember before purchasing him I read a lot of people say firemouths were really slow growers, and they weren't wrong one bit!
I have a similar setup, although my jack is only 3" and is bullied by the FM and the smaller convict. I'm sure that will change though.
How is the interaction between the JD/firemouth on any given day?