I keep hearing they're pretty useless for dealing with algae, because of not wanting to wipe out what they perceive to be their only food source. But hells yeah they are way adorable, I love these guys.
I recently got 8 RCS for my 20L (I meant to get 10, but the store was lacking). I have an abandoned 1.5 that I'm planning on setting up as a species tank for the little guys, so they can breed safely, and maybe I'll set up a desk shrimp so I have someone to look at during most of the day. I have a big ~1L vase that I failed to turn into a mini-riparium, so I think I'll use that, but not fill it all the way. Any advice?
I have always found my RCS to be good algae eaters in the sense that they keep the tank spotless of debris of any kind (I'm probably wrong, but I think excess debris helps create algae). I've also seen them picking at any type of algae I've had. Now, does that mean they'll gobble up loads of BBA, hair algae, and staghorn algae? No, but they'll try (unsuccessfully for the most part)! They get extra points for trying, right?
I regularly feed my hundred+ RCS and they still manage to keep my tanks nice and clean. Most people suggest feeding RCS very rarely, but I just do what works best for me. I do have lightly stocked tanks, so that may be why the RCS can keep them clean even when fed often. It is quite entertaining to see them slap-fight over food, too.
While you likely know the following, I'm going to post it anyways:
For the 1L vase, stocking numbers depend on if the vase will be heavily planted and/or actively filtered. Once it is set up, you may want to wait until you have a healthy colony in one of the other tanks before testing the waters (literally) of the vase with RCS. While RCS are hardy for a shrimp, they are not indestructible. For example, it's a bad idea to do what I am currently doing in my nano bowl, but I have so many RCS that risking three is not even of consequence to me.
I do have one question for you, why do you plan to not fill the vase completely?