For me the weeksii has to be my slowest with a consistent slow growth rate from the get go when I got it at 7”. Its fairly thick now but only about 15” or so after many long years. My next two slow growrs are my laps, both the Faranah and Koliba were moderate growth to about 15” and have grown super slow at this point. Been trying a new round of power feeding and water changes but they still seem pretty slow.
Probably the lack of Massivore in the diet is one reason. When I was power feeding them with it they packed on serious size quickly but they looked fat and unnatural to me so went to natural stuff like tilapia, shrimp, squid, krill. My polys look leaner and healthier now.