Hi Kassandra and welcome to the forum
How long has the tank been set up for?
How long have you had the shrimp and snails?
What sort of filter is on the tank?
How often and how do you clean the filter?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate (looks like sand) when you do a water change?
Do you dechlorinate the new water before adding it to the tank?
Don't add any new fish, shrimp or snails until this problem is resolved.
Don't add any bottom feeding fish either because they will starve. The shrimp and snails will deal with any food on the bottom.
If a fish ever gets sick or the tank doesn't look right (cloudy water), do a 75% water change and gravel clean the substrate every day for a week, or until the problem is identified. If you have sand on the bottom of the tank, just hoover over the top to remove any uneaten food and fish waste.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
You need a picture on the back of the tank to make the inhabitants feel more secure. You can buy aquarium backings from any pet shop or online. You can also use coloured card, newspaper or a plastic bin liner. Just tape them to the outside on the back of the tank.
Some floating plants like Water Sprite (Ceratopteris thalictroides/ cornuta) would shade the tank and encourage the shrimp to come out more. More live plants growing in the substrate would help too. Some good plants to try include Ambulia, Hygrophila polysperma, Amazon sword plants, narrow Vallis.