stunted growth

So I have had my Yoyo Loaches since February and some of them show good growth. Others are the same size as when I purchased them. The largest one is about 3.5 inches and has doubled in size since February. The smallest is not even 1.5 inches, I don't think it has grown at all in the 6 months...

So I thought I would keep you guys posted since the last posting rampage where I spammed updates (sorry, :P). Anyway, since then the fish got a 60% water change and I've really seen some growth but not sure if they've passed the effects of early stunting... I'm doing another water change...