Hi and welcome to the forum
Normally males have longer more pointed dorsal and anal fins, and the females have shorter more rounded fins.
I don't recall blue acaras having a yellow edge to the dorsal fin but it's been a while since I saw them. My understanding is the yellow edge on the dorsal fin is from breeding blue acaras with gold edge rivulatus (green terror cichlids). I might be wrong and really need my books to check.
Hopefully our cichlid specialist
@Wills can help.
The fish on the right looks a little sunken in around the belly. If it is eating well, the fish might have intestinal worms. Section 3 of the following link has info on treating fish for intestinal worms.
Fish do a stringy white poop for several reasons. 1) Internal Bacterial Infections causes the fish to stop eating, swell up like a balloon, breath heavily at the surface or near a filter outlet, do stringy white poop, and die within 24-48 hours of showing these symptoms. This cannot normally be...
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