see pet shop tanks will always have lots of red spots in them.
things that go on behind the scenes - WC's every day, controlled feeding, Gravel Vacs every 2 days, nets in and out of the tanks throughout the day disrupting the fish, lots of filtration.
we cant tell you what to do, and we all hope that you will as you have said, either get a bigger tank, or re home them when the time comes. Im just a little taken aback with what you were told about how they would not out grow your tank for 2 years.
I get mine about the same size, and they usually get to about 6 inches within 5-6 months at most. and in a 4 ft tank, that's when i pass them on -so they can grow well and have a nice sail fin like the real good ones should.
wish you the best of luck with your fishies