How long did you have the yellow fins to get them 18" ?
about a year and a half to get them that size. they grow very fast.
the ones I have now will take longer as there is more competition for food because there is more of them. I figure that when they get large I will sell a few of them off. my tank is not big enough for all those barbs at full size. no way. I have to cut the numbers back a bit.
but I have time still. I figure even at 10" in size each that tank is large enough to handle that many. but beyond that, I will have to sell.