Ok so now that I think of it if this is occurring consistently regardless of lights were just turned on I think this suggests that what you have is more than likely a Blue Acara or a electric blue with poor or weak genetics. Let me explain as my wording isn’t the best. The Electric Blue Acara is a hybrid which is produced from female electric blue ram eggs which are fertilized by a blue acara male. From this select offspring are then chosen to reproduce to try and strengthen the look that we see in an EBA. Occasionally a blue acara is later bred to one of these offspring females again to introduce some fresh acara blood and to reduce the inbred blood. Now as I ve kept these on 2 seperate occasions this being the second time I ve never seen any black lines or spots on my EBAs.
So to clarify I just think the specimens you have may just not be the most ideal offspring from breeding process. Could you post a few pics of yours in this thread ?