I use a black marker, because I happen to have it. The jars are
ALL labelled other than the newly jarred aka N/A which then I ended up labelling n/a1, n/a2. When the pictures are taken they do not always swim up close to the numbered area, which then when I take pictures it actually takes a half hour to write down, upload, and rename every single picture to the according fish. Why the different brightly colored markers? Black works for me, and I have the males and females who are jarred in different areas (females left, males right) along with the unknowns in the center, between male and female.
All fry of this age are fed twice a day. The smaller tummied (greedier) ones have been jarred, such as the last jarred one who devoured way too much in the tank and was floating around awkwardly. They get their thawed bloodworms, and NLS small fish formula pellets.
Is there a problem with "confusion" with the 150+ fry in the grow out? I was told not to jar them all. So I didn't. Some that I have pictures of, I know which are which due to the coloring that has stayed or their characteristics in swimming, or behavior even, along with minuscule differences in their finnage - such as one fry has a streak of red, where a similar one does not, on the caudal on the bottom.