Thanks Phillip and Ricardo.
I regret now for not buying all the 7 discus Galaxy RT.
They came up much bigger and beafier than the melons.
I'm also tempted to hand measure them , but I haven't got the guts yet . I did measure my smallest hero discus when I was transferring him to QT with new arrivals and he was 4.5 inch.So my guessing is that RT should be around 6 inch since they look considerably bigger than him.