Who Gives A Fish Forums

I've got a bit of a dilemma on my hands. I picked up 7 Dwarf Neon Rainbows a couple of days ago (11th Jan, to be exact), and they're tiny - about 2cm each, with some looking really underfed from the store. I'm thinking of adding some larger Dwarf Neon Rainbows to the mix, hoping the stronger fish will help create a solid school, making the smaller ones feel safer and reducing stress-related issues.

My main concern, though, is that the older Dwarf Neon Rainbows will school with the younger ones but outcompete them for food. I'm pretty sure I know the answer, but I'd love to hear your thoughts.

A bit of context: my tank is 300L, heavily planted but with plenty of open space. Tankmates include cardinals, Otos, sterbai and peppered corys, 2 red honey gouramis, and a very shy bristlenose.

As for why I bought the small Dwarf Neon Rainbows in the first place... I got them from Pets at Home, a UK pet store chain I've vowed to avoid after a bad experience. But I was in there for fish food and stumbled upon the rainbows. I just couldn't leave them behind, thinking they'd end up in someone's inadequate tank. So, I took them home, and now I'm trying to figure out the best way to care for them.

Honestly, I've never been too fussed about fish competing for food, mainly because I've always erred on the side of caution and overfed them. To counterbalance this, I tend to do more frequent water changes and occasionally skip a day or two to give the tank a break. I think if you were to overfeed for a short period to help the new fish bulk up, it wouldn't be the end of the world, as long as you're on top of water changes and have a solid filtration system in place.

Edit: Don't get me wrong, overfeeding's not a good habit to get into - I'm just a sucker for those pleading fishy faces.

I'd advise treading carefully. You need to figure out why these Dwarf Neon Rainbows are underweight in the first place. It's natural to feel for struggling fish, but buying from a big-box store without a quarantine tank can be a recipe for disaster. Adding larger rainbows to the mix might put them at risk, especially if they're not as healthy as they seem.

Ideally, I'd have isolated them for a few months in their own tank to monitor their health. Unless the new fish you're considering looks incredibly healthy, you're taking a gamble by introducing them to your tank. You want to see if the current fish can gain weight with regular feeding or if they're dealing with a wasting disease. Not everyone has a quarantine tank, so buying the healthiest-looking fish from reputable sources is often the best defense. Rescuing sickly fish has led to tank wipeouts for many aquarists.

Heavy feeding might not be the way to go here. Dwarf Neon Rainbows enjoy their food and shouldn't need coaxing. They're slow growers in terms of length, but they should develop a healthy body weight quickly if neglect was the only issue. Keep an eye out for signs of illness, such as bent spines, sores, or an inability to put on muscle.