Welp, I just went through all of my photo's from July and the ones that are the best/most usable are from the middle of July, so by then I'd had my little juvies for 2 weeks. They'd already grown over a 1/2" by then, but the pics will still give you a general idea of how small they were compared to the 6" older group.
Oh and I removed some of the plants and driftwood just before these pics were taken. They needed a good cleaning and stayed in a QT tank for a few days till I could get around to do that.
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Growth rates on both batches of discus have been right on par for all the groups I've grown out in the past 5 years. I average about 1" per month till they reach 5", then 1/2" per month till they reach 7", then they add another inch or two over the course of the next year of life.