Shrimp and crabs in the over flow

[Zippo1313]

Hello I have a 120 drilled tank that I am using for fw ca and sa cichlid tank I'm going to be making it a coast to coast over flow set up that I was going to make a little bit on the big Side so that there will be about 3 gallons of water in there at all times I'm making it clear to now here is my question has anyone ever tried to Keep fw shrimp or crabs in there overflow what do u all think let me know if u have did it work if not why didn't it work thanks to all

 

[Zippo1313]

Anyone please and have another ? What is the best way to remove purple alge from glass with out scratching the glass