geophagus tapajos

Hi guys, So I got an upgraded system recently for my fish. I have 6 x geos tapojas, 2 x severum, 2 polyptrus senegalus. Tank is 130 gal (1.8m x 50cm depth x 60cm height). Filter is 2 x sun sun canister filters, 2000L per hour each. Plus an internal powerhead filter. I originally got this...

title says it all - they are 4 months old now, received as small distinguishable inchlings. They are quite expensive here so I only got two- hoping they are male and female. They have only just started to change colour, and a lot. Both of them equally. Not sure if you can tell yet which is male...