Join Date: Jun 2010
Location: Jakarta, Indonesia
Sorry your fry are having problems. Hope they make it to adult.
TBH, your fry looks OK to me (both in picture and video). Not sure if the picture isn't really showing fry's real appearance. Remember, I'm not there. You are. So you have to trust your instinct/judgement.
I'm not sure what the spots are. They may be first sign of color. You are there to see them (I can only guess from explanations and pictures). The first signs of trouble are clamped fins and lethargic fry. Then they will lose their appetite and swim oddly (by the time they act different would probably be too late and you will start losing some).
You did the right thing by taking precautions. But if fry are not lethargic, I'd reduce medication to "prevention" (usually half of med). Not sure how reliable this is; some say copper based meds may do more harm than good. I've never used it on small fry but used for 2.5 cm and above hasn't given me problems except (MAYBE) betta becomes dependent on meds.
I wish you the best of luck. Hope they grow to adults.