Could hormones naturally released by growing fish have built up in the tank, which inhibit grow rates? I've had some purchased young Synodontis decora since mid summer, bought at ~4cm TL, which were given ~50% weekly water changes in their original tank. I was baffled why one or two had doubled in length and girth, while one was barely any bigger than when bought. I then increased water changes when they were transferred to my 48x12x15 a couple of months back, doing 33-50% at least twice a week and now the whole group are growing much quicker.
Are you adding three or four small meals per day? Could the Kribs benefit from a change in diet to say Tetra Prima as their staple? I have ~35 Lionhead Cichlid fry, born about six weeks ago, that were ~1cm when they emerged for the first time. They are given four small meals a day, mainly Tetra Prima but sometimes Hikari algae wafers and catfish pellets to mi things up a bit, they are now just over 2.5cm long and deepening up quickly.
