I didn't find you guys in time to deter me from buying shrimp in a pre-packaged ecosytem. However the ecosytem I bought isn't sealed--I knew enough to avoid that--it has a cork that you can take off to care for the shrimp. I have four shrimp in 250 ml of water, with the algae and sand/shells/rocks, etc. that were included in the kit. So far, the shrimp seem to be doing ok--they're always busy and sometimes zip around their ball.
Question for the hive mind: Since it's a semi-closed ecosystem and I can intervene if there's an issue and feed the shrimp when necessary, do I need to worry about the size of their enclosure? Do four shrimp need more room to roam, or will they be ok in their 250ml? Should I toss the cork altogether and just leave it open for them?
That's a really small system. I suggest something larger, so think about reading up on how to set up your own tank and then transfer them after the new tank has cycled. Air exchange is necessary so I would ditch the cork and then add distilled water as needed to make up for evaporation loss. I think 2 to 5 gallons is a nice size for these shrimp.
Sorry that you didn’t find a deterrent in time, thankfully you only have 4.
I agree with sliphorn that the current amount is far too small. While they could probably survive for a while they will be slowly starving to death. There isn’t enough room to grow enough algae to sustain them, and to compensate they end up absorbing their own body mass to survive.
For perspective Mustafa’s guide to setting up their home is a tank that is at least a half gallon in size, which holds approximately 1893 ml, 7.6 times larger than what you have them in. The guide actually says a gallon or larger is better but for argument’s sake since I don’t know what spatial limitations you have and because I recall others on the forum who do keep them successfully in the 1893 ml sized tank. The larger tank is encouraged in part because if something gets into the water having a larger tank reduces the concentration and increases the chance that the shrimp will survive the contamination.
In short it is time to go shopping! I would offer to give you some of my leftover sand and small shells if you are local. I’m in the northeast area of the United States.
You can pick up a 1 gallon tank at Petsmart for $14.95 that comes with a hood w/light and a filter that you don't have to use. I have mine in one of them and they are doing well so far. 250ml is only slightly more than a cup, 8oz, and I would say that it's too small.
Hello all! Thanks so much for your advice. I am a bit limited with space, but I did go pick up a 1/2 gallon container with a light that I'm going to start today, so hopefully as soon as I get the new tank set up, I can transfer my 4 shrimp into a better ecosystem where they'll be happier. I took sliphorn's advice and removed the cork--they seemed like they perked up after about 20 minutes. I'll do my best to make sure they stay happy!
However the ecosytem I bought isn't sealed--I knew enough to avoid that--it has a cork that you can take off to care for the shrimp. I have four shrimp in 250 ml of water, with the algae and sand/shells/rocks, etc. that were included in the kit. So far, the shrimp seem to be doing ok--they're always busy and sometimes zip around their ball. 
