One Of My Mollies Is Not Growing

About 3 months ago I got 2 male Dalmatian mollies from my local aquarium shop and one of them has not grow much, if at all. The other one, however, has about doubled in size. I have 5 other goldfish in a 30 gallon tank. Ph is around 7, temp. around 75F. I feed them tetra flakes and some pellets for the bigger fish, and the smaller one is able to try to eat some of the flakes, but ends up spitting most if not all of it back out. Recently, I've noticed the bigger molly will chase the smaller one relentlessly and almost looks like he's trying to eat his fins, as some of them are tattered at the edges. Please let me know if there is anything I can do for the poor guy! Thanks!

 

What are your ammonia, nitrite, and nitrate levels? Regardless of the type of Goldfish, you shouldn’t have 5 in a 30 gallon. If they’re comets or commons, you’ll need something like 150+ gallons.

Can you post pictures of the Mollies?

 

Ammonia levels at 0, nitrate at 5ppm.

 

Some of them just take longer to catch up, some never do or are stunted or don't have the best genetics. Whenever I have fry (mollies, swordtails, platys), they always grow at different rates.
They don't look sick, so I'd say it's just normal size variation.

 

It appears you have a male and a female. What could be happening is that he’s trying to mate with her so much that it’s stressing her out. The general rule for live bearers is to keep them in a male to female ratio of 1:3 for this reason.

 

Oh wow that is interesting, I've always thought they were both males, thanks for the info everyone!

 

Oh wow that is interesting, I've always thought they were both males, thanks for the info everyone!

Hard to tell from the pics, they could both be male (bigger one definitely is, would need a clearer pic of the smaller one to be sure), but either way, the size difference is fairly normal. They could be from the same lot, or could even be different ages or unrelated -it's not uncommon to have a tank full of growing fry and then add the next lot when they get big enough to join the older lot and so on, before being sold to the shop where you got them from