Reddish Color On Silver Mollies

[Samsonite]

I have had a 55 gal tank that I have been taking good care of but lately I've notice a few of my mollies have reddish orange spots on them, near the back of the fish. The fish I currently have in there are 6 Silver mollies(2 male 4 female) 6 guppies(also 2 male 4 female), 4 neon tetras and 2 lemon tetras. Also have 3 pleco fish about 4-5 inches in size. The tank is never dirty and I always do 1/4 water changes every 2 weeks. Theres a lot of silver molly babies that are about half an inch and a lot of guppy babies as well also under half and inch, as well as a few newborn ones. In all id say theres about 60 baby fish. Is stress the reason they ahve those reddish orange splotches on them? Im going to get rid of the baby fish asap since its overcrowded. And if not, what is the reason for those splotches.

 

[NickAu]

Wow talk about overstocked.
 

 
The tank is never dirty and I always do 1/4 water changes every 2 weeks.

With your stocking levels I think 50% every week is needed.
 
Can you please give us your water parameters?
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:

 

[nic1]

do you have a picure of them?