Depending what shrimp you decide to keep, a 29 has space for a lot of variety and a lot of shrimps. If you plan to plant it heavily, and use some wood and rock, the shrimp will love it, and it will provide a lot of feeding area plus hiding areas for babies and shyer shrimp.
You could have a few different species of dwarf shrimps, which would let you have at least 3 different colours, and there are also small species of Fan [ filter feeding] shrimp that are close to the same general size as Neos [ Neocaridina, aka Cherry shrimps ].
One of these would be the Green Lace Fan [Atyoida pilipes]. Females in this species are much larger than the males, and each sex has completely different body markings, which are quite attractive. There's also the Golden Fan [ Atyopsis spinipes]. A. spinipes also comes in the wild form, which has a paler body colour, [many are a pale yellow], with their longitudinal stripes being so pale they're barely visible. Their 'fans' are hard to see too, being super small, but the main species variant, called Golden Fan, have larger fans, a golden body colour with reddish body stripes. They are remarkably similar in appearance to the large Bamboo shrimp, and could be mistaken for a young A. moluccensis, if you don't know what to look for.
The small fan shrimp often seem to enjoy lining up in rows on the substrate to filter feed. But they will also hang onto plants, rocks, even other shrimps, to catch a sweet feeding spot. I've seen several of the tiny fan shrimp sitting on top of one of the larger species, making a sort of shrimp pyramid, all fanning away in the same current.
To keep fan shrimp happy, you really need an interior circulation pump that runs independently of the filter, to provide enough current for them to filter feed in. I use a Hydor Nano pump for this, personally. You'd also need to provide foods that suit their feeding style. Live foods are very much appreciated where possible, mainly microworm or other really tiny worms and cultured green water, or single cell algaes, such as Nannochloropsus, Chlorella, etc. These algaes won't turn your tank into pea soup at all, you don't use too much of them. I used a big syringe to inject about 100 ccd of cultured green water just in front of the pump, twice a week, to keep my filter shrimp and clams happy. Then I turn the filter off after feeding any special food for filter feeders for about an hour, while I leave the circulation pump going, to keep pushing the food around the tank, so the shrimps get a good shot at filtering them out.
You can also feed frozen BBS, and fine particle dry foods, like Golden Pearls in the 5- 50 micron size [ invented to help replace BBS], also NLS Small Fry Starter, spray dried algae, like powdered pure spirulina]. Dry foods should be mixed well with water before feeding for filter feeders. These foods are also excellent for very small fishes and tiny fry.
You can only have one colour variant of the Neos, if you want the babies to be the same colour. Allowing different coloured Neos to breed will give you wild form babies, which are dull brown or colourless.
So a way to get variety of colours in the small shrimps is to keep similar looking species that need the same general conditions, but cannot cross with Neos. One of these would be Caridina propinqua, aka Sunkist shrimp. They are bright orange & look a lot like orange Neos. They too have larvae, and so far as I know, their larvae need salt water.
Another species that would suit is called Babaulti. A bonus is that they have babies just like Neos do, live mini adult forms. They come in a few colours, an attractive olive green being the one I've seen most often. I've also seen them in 'assorted' colours, where some adults were orangish and some were green and perhaps another colour too. Only saw those one time, but I was told they reproduced babies in the same colours as the adults. Can't cross with Neos or any other of the species mentioned here.
You could also toss in some Ghost shrimp,[ the American one, palaemonetes], which gets along with all these others, and may well give you a few babies too. Though they also have larvae, their life cycle is entirely in fresh water. Depending on temps, and other conditions, they take 4-5 days to morph into the adult form. With a bit of luck, you may get some growing up to mature size, as I did in a mixed community 29G. Be aware, Ghosts have been known to eat the odd baby shrimp, but not so many and when I kept them together, with Snowballs, the white form of cherry shrimp, it did not have any appreciable effect on the number of baby Snowballs that grew up. I even had fair size fish, including cories and danios, in that tank. It surprised me that any baby shrimp survived, but loads of them did, and I had maybe two or three little Ghosts grow up every couple of months too.
There are also some large fan shrimp species, which are much larger than the other species I've mentioned, but are quite harmless despite their size, and they don't mind smaller shrimps being around, or even sitting on them. Bamboo shrimp, aka Wood shrimp [ Atyopsis moluccensis] and Vampire shrimp, aka Giant African Filter shrimp [ Atya gabonensis].
You would not want too many Vampires, they get to to 5-6 inches & prefer their own little territory as adults. Youngsters hang out together, mine even hang out with the Bamboos. Often a slate blue, can be tan, grey, white [ rare] or paler blues.
Bamboos, full grown are 3 - 4 inches. Males of both species have a much larger, thicker pair of first walking legs. Male Bamboos also grow a prominent hook on the back of their main leg joint. Vampires have loads of bristles and bumps as well as a seriously heavy pair of first walking legs. Often shy, but given enough hiding places and other shrimp such as Bamboos, which sort of act like a dither fish does, I think, they will come out and be seen. Fan shrimps like the same general conditions as Neos do, alkaline pH, up to about 7.5 or a bit higher may be tolerated, with coolish temps [ 72-74F] & hard water, needed so they can moult properly. All enjoy heavily planted tanks, with plenty of rocks & wood for extra hiding places & perches to filter feed, and almond leaf litter is appreciated by most shrimp too. Once they become skeletons, replace the almond leaves.
Depending on how much you hope to breed, fan shrimp are a real pain. They have larvae which require salt water to survive, and may take 90 day to morph into the adult form, which is quite a challenge to manage. But given good care, they can live quite a bit longer than many dwarf shrimp.
You'd want to cover a Bamboo's tank, as they will try to take a walk now and then. This usually proves fatal unless you are lucky enough to catch the shrimp before it dries out. In nature, they hike from one small pond to another, presumably for breeding advantages and I assume that's why they go walkabout. Sadly, they don't know the tank is the only pond in town.
If you find you miss fish, or maybe the middle to upper portion of the tank isn't as lively as you'd like, you can also keep a few species of fish. Very small fish usually don't do too much damage to baby shrimps. Otos are the only fish said to be 100% safe with shrimp babies, but since the shrimp also eat algae, the Otos may not get much to eat.
Strawberry rasboras are a delightful, super tiny fish. Similar to the Chili rasbora, which is another tiny fish that's brilliant red. Chili's seem to tend to be rather shy, and often you won't see much of them. Strawberry's are not so bright, very tiny, 3/4 inch or less. With such a tiny mouth, even baby shrimp would be a big bite for them, and they tend to be mid level or surface feeders. Both sexes have a black blotch on the side, with the females having just a tiny dark spot and males a much larger one. Females are rounder underneath and slightly larger, with less colour than males. A tight schooling species, so they like their own company. You could have twenty or more of these tiny guys, plus shrimp, in a 29 G.
Or there's the Galaxy rasbora, aka Celestial Pearl Danio, [now classified as D. margaritatus]. Bit more than an inch at maturity, they may well eat the odd baby shrimp, but not a great many of them. Males tend to spar and it's best to have 3 or so girls to one male. They do best in heavily planted tanks with well broken up sight lines. Males are lovely, a rich dark blue w/ tiny white spots, red fins w/black bars. Females much duller, paler blue green, w/white spots, yellow on the belly, no red fins. Males coloration gets really intense if they are courting females.
