Petrochromis Trewav full size

[petro101]

Hey guys, curious how long it takes for a petrochromis trewavasae on average to reach full size? I know diet and maintenance plays a roll into getting them to grow quicker... mines grown about 1" in the last year. I feed him high protein pellets (52%) i got from Alex at ultimate fish and I do 50% WC every week or every other week. He's about 3 years old pushing 5-1/2". Do these guys stop growing at a certain age? If so what age should they be at full size?

Thanks!