Also, since the hobby mollies are an amalgam of three or four mollies species, most of them tropical, it might not be a surprise that they don't really thrive until about 78-80 degrees F./ 25.5-26.6 C. Fish that are relatively cold, don't grow much in the winter.

Lastly, the hobby is riddled with stories of dominant males releasing "growth-suppressing hormones." While that is possible (heck some plants release allelopathic chemicals which inhibit the growth of other species of plants and can even kill them) water which hasn't been changed much will gather a lot of nitrates. If there are enough nitrates in the water, they will seep through the gills and into the fish's blood. Nitrogen compounds can keep hemoglobin from carrying enough oxygen for the fish. (In some cases the fish slow down, settle on the bottom and eventually suffocate. That is called nitrate poisoning.)

Even if a fish doesn't die, if they are not getting enough oxygen, they aren't effectively metabolizing the food or growing. They can stunt.

That, as can chemical warfare between plants and even nasty wars between saltwater corals can be blunted by increasing the frequency of partial water changes. For headwater fish like guppies, they may get 90+% water changes daily.

So raise the temperature. Feed them a variety of foods. Leave them a veggie tablet or the inside of a cooked pea to nibble on. (They are almost constant browsers in the wild.) If you have a tank, plagued with hair algae, try them there. Try for that goal of 45% weekly water changes. Keep your filter efficient.

You also mentioned something about the mollies being in saltwater. Is that made up with a marine mix (which includes many other important and necessary minerals)? Or is it just sodium chloride, which actually might leach essential minerals out of their bodies?

Editorially I wish you would take the time to include sentences, periods and other punctuation in your posts. I think you would be even more understandable. If you think that is an unfair request, what is the primary grade where your local schools begin training students to use capital letters, sentences and punctuation?

I think the issue is just laziness and an unwillingness to bother with those things here. In the real world, what kind of occupation would writing like that on a job application land you? What would people you wish to cultivate or be friends with, think your opinion of them is, if you are so slothful in your communication?

I know of several pretty good aquarium forums and mailing lists where your questions would be simply ignored because the list members would assume that you either couldn't or wouldn't write a coherent sentence. They would feel quite disrespected. I think you have some really interesting thoughts, you are learning and asking some tough questions. That indicates to me that you can do all of that basic mechanical stuff. ;)

Please give it a try.

You couldn't be a worse speller or typist than I am. I think highly enough of you to clean up as much of the mess as I can with spell and grammar checking and proofreading.

When I know I have slaughtered a word like allelopathic, I copy my first try and paste it into Google. If the spelling is close, Google will ask, "do you mean ...." I click on their suggestion and see if the word is used the way I think it should be used. I am  also busy enough and lazy enough to take handy shortcuts like that.