Yikes! That could be ammonia burn of the edges, a bacterial thing or, if they are clamping, velvet. That could be partly because, if your tanks are under 9 weeks old, they could still be cycling.

Every time we add fish, that ammonia equilibrium will slide off balance. That is why adding a few fish at a time is better than adding a lot. There will be a bubble rising in you ammonia, then nitrates and then nitrite levels all over again.

You may wish to season you water longer, try to work another water partial water change into your busy schedule and maybe add plants (if there is light) or put something into your filter to absorb some of the ammonia.

It may sound gratuitously mean-spirited for someone else to say that to you. (I'm fascinated by work, so long as someone else is doing it.) Not trying to be that way. Just want your fish to thrive and you to enjoy the hobby. :)

Miskairal's point is well taken about convenient numbers, but again these fish aren't evolving for survival in aquaria, but in nature. (And to the extent that professional fish breeders play a role, they are probably trying to produce more prolific females.) If a pair or two of offspring survive to reproduce in the wild, the female and her consorts have done well.

In comparison to the 20/25 per female per month in your tank, at the moment, or the 90 per month in the case of Angelhologram's late bloomer, most egg laying fish need to produce far more eggs for there to be a breeding pair produced for every breeding pair giving it their all. The only exception would be some of the mouth-brooding cichlids. Especially in the case the Lake Malawi mbuna, their eggs and fry are even larger than baby guppies. There are even fewer fry, but by the time they are finally released from the shelter of the mother's throat sack, they are big enough to eat baby guppies.

How big the egg or young is, where the young are produced and how developed the off spring are, will have a lot to do with how many are produced. So a pair of killies will produce 10 to 70 eggs a day. (Or 1,200 a month.) Tetras may produce even more, on a more or less daily basis. Big cichlids with open nests on the substrate will lay 100s to 10,000 eggs each spawning cycle, which in the wild could be 1 to 3 months in interval. A mature ocean going codfish female will produce a couple million eggs annually.

The largest bony fish is probably the two-ton adult ocean sunfish (Mola mola). Living to maybe 100 years if they get past planktonic stage, they can lay 300,000,000 eggs a year. They are about 2-3mm in diameter or roughly three times that of a guppy, double that of than angel or 1/3 bigger than the eggs of the golden wonder killies (Aplocheilus lineatus).

By the way, there are many families of livebearers. Only about four families of livebearers (Poeciliidae, Goodeidae, Anablepidae - the four-eyes - and the Hemirhamphidae - the halfbeaks) commonly kept in aquariums. The freshwater stingrays might be number five, but one needs huge aquaria, better yet large family room ponds, to properly care for them.

Over a 1,000 species, worldwide, are livebearers. Several shark families are livebearers too. A female Great White may drop as many as a dozen youngsters, already about 5 feet (1.5 meters) long! (But see "Are All Livebearers Conceived, Carried and Born the Same Way?")
http://www.guppylog.com/story/2003/11/11/203510/74

And you thought your guppies had babies! :)