Newt Runt Getting Bullied

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I recently got four ~5 month old T. Dobrogicus. Three of them have grown much larger, but one is still very small. When I got them, she was about the same size as the other newts but a bit fatter. I feed them all by hand, so I know she's been eating, but she's still tiny. I've also noticed that she tends to float at the top of the tank for a good amount of time after eating, so I'm not sure if that's something to worry about or if it's just a sign of a gassy newt.

A couple days ago, I came home from a day trip to see she was missing a chunk of her tail. Her tail has always been noticeably shorter than the other newts', but now there is a small dip on the top of it near the back. I wasn't sure if this was caused by a fellow newt or if she'd found something sharp in the aquarium, but today I saw one of the larger newts bite her tail and her side before I could separate them. I'll attach a before and after picture of her tail.

My newts fight viciously during feeding time (which is why they're fed individually now), but until recently I'd never seen them bite each other unprovoked. Should I take her out of the tank until she gets bigger? I don't have a second tank on hand, so I'd have to either wait until tomorrow to buy one and remove her or put her in an emergency large Tupperware until I buy her a new home.

Some specs for those interested:

• Eating pellets (provided by breeder) and bloodworms either daily or every other day. Introducing daphnia and BBS this week.
• Four newts in a 30 gal with a filter and weekly water changes
• Ammonia at 0.25 (working to reduce this)

Also, should I be concerned with how tiny she is? She's eating well, but seriously this girl is just not growing.

Thank you!

 

[Chinadog]

I would separate the smaller one asap, young Triturus are very good at ripping bits off each other so the smallest one usually catches the worst of it.
I wouldn't worry too much about its size or the floating just yet. If its eating and growing, even if it's slowly there's a good chance it will catch the others up. I've had runts in the past that have turned out to be healthy, robust adults, it just takes a bit longer.
Hope this helps.

 

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Thank you! I'll make a trip to PetSmart ASAP. Would a 5 gal without a filter (and frequent water changes) be okay, or should I set up more of a long haul type tank?

 

[Chinadog]

I think a single juvenile would be fine in a 5 gallon, but only if you can control the temperature. Small tanks gain and lose heat fast so water temperatures can fluctuate quite a bit which isn't good for Triturus. I would fill it full of aquatic plants and keep a careful eye on water quality, levels of waste can rise very quickly in a small tank.
Maybe a temporary divider in the tank you have would be easier?

 

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Oh, I hadn't even considered a tank divider! That's a great idea. Thank you for all your help!