Blue Acara, right?

[japes]

True in your examples, however even the OP's photographs show an off-centre blotch, similar to the Gold Saum you've just used as an example, though perhaps not as elongated.

Googled example compared to my old female Aequidens pulcher

Regardless, the easiest way of telling the difference between species is the orange caudal band. If you can observe the species swimming you'll also notice (as is also confirmed by your Gold Saum image) that juvenile Aequidens sp. "Gold Saum" very often swim with their pelvic fins extended, whereas Blue Acaras do not.

 

[Otherone]

Good point

 

[CeD_^]

from what i have learned, gt have the orange/red color on the tail and caudal fins whereas the acara not. also, if you look at the scales, gt's scales are aligned horizontally compared to acara. can anyone comfirm plz?

 

[japes]

Blue Acaras can have the orange/yellow lining on the dorsal fin, as well as a much thinner orange/yellow lining, generally only in the top third along the edge the caudal fin.