Sudden bully

[SaraB]

So last week I had a fry die, I didn't think much of it until I saw one of my juvenile mollies attack the other and then start trying to nip at a platy fry.
I stuck a heater in what was going to be my 20 gallon coldwater tank and did a few water changes to bring up the temperature. So she is in there right now (not happy being by herself).
My questions are
1. Does a time out work for fish or will she be worse if I put her back
2. Is my tank overstocked and is that causing the issue?
3. If no then will adding more hiding spots work ? Or should I sell her? (last resort)
4. If no then is there something I can put in the 20g that will make her less lonely but also something that she won't pick on?

My main tank is
55 gallons with 5 adult female platys, fry of course, 10 black neons, 3 cardinal tetras, and the 2 leftover molly juveniles (only 1 now that I moved her) from when it used to be a molly tank.
Ammonia 0
Nitrites 0
Nitrates 10ppm
Temp 78f

The 20g is
Just the 1 molly juvenile (clementine) and some baby mystery snails (hitchhikers)
Ammonia 0
Nitrites 0
Nitrates 5 ppm
Temp 75f (preset heater)

 

[Autumnsky]

That amount of fish even with fry shouldn't be overstocked. Let's say that the possible multiple feedings might have been a lot and the water parameters were out of the safe zone before the testing it can cause aggressive / attacking behavior. But if that wasn't possible, or the case, then you might have a mean fish.

A time out can encourage fish to behave in Goldfish.

Not sure of Mollies. Also a maybe she could be upset by so many fry swimming around, she didn't get enough to eat... I am reaching here not sure at all. Maybe needs a pinch of salt. Had a tummy ache. Or mean.

You might try and add her back in and see how it goes, basically being there watching for a long while to see if all is well. Adding her back in, as you would guess is a gamble.

She might act okay for awhile - during your observation time, then go rogue again when you aren't there to step in. When I had a mean fish I gave him to a person with a tank of bigger "semi aggressive" fish (not mean fish though) and it behaved itself like an angel. No more bullying.

 

[SaraB]

I only feed once a day, should I feed twice? I feed first thing in the morning with both flakes and pellets to make sure everyone gets something. They get frozen live food once a week and I'll occasionally treat the mollies with a sinking algae tab.
Unfortunately I had to add her back in. My one platy developed a swim bladder issue so I switched her into the 20g for her safety and so she could recover and put the molly back in the 55g.
The biggest fights seem to happen with the other juvenile molly (female). Is this just a random hormonal thing? Like are they just trying to establish who's the "alpha"? Of so would adding an adult female molly put them in their place? Or would it make things worse?

 

[Autumnsky]

Mostly I have kept Platy and not positive on the best course of action. They were so numerous it was hard to notice anyone not really getting along - mostly busy in the mating department, even very young :/. And that may be a clue. (the getting hormonal at an early age.)

 

[SaraB]

It definitely didn't look like mating. Lot of tail slapping and attempted fin nipping.
I'll keep my eyes on it and if it doesn't get better I'll sell the more aggressive one as a last resort.

 

[Autumnsky]

Meant more like the part of hormonal increase towards maturity as a maybe. Agressive /bully fish don't work for me either, I'd agree if the behavior keeps up to rehome.

Try a few more frequent pwc and do you do a bit of salt in the tank? Since I hear they can adapt to SW I'd imagine they would like some. The