Why Are My Shrimp Hiding?

[Lukes Shrimp]

In my 7.9 gal aquarium I have some cherry shrimp, 2 tangerine shrimp, a pumpkin shrimp, and an amano shrimp. I've only had the tank for 2 day and I woke up this morning and they were hiding somewhere. I definitely can tell something is wrong because the amano shrimp isn't coming out like he usually does. The only ones not hiding are my tangerines and my pumpkin and 1 cherry. I have a heater that is set to 75 degrees and lots of plants. I have no fish. Please help me so I can fix this ASAP. My filter isn't the problem 'im pretty sure. Thank you for your time.

[Mustafa]

If you've only had the tank for two days, that means your tank is not cycled. Your shrimp are probably hiding because they don't feel well. Look up "cycling a tank" and research this website with the "cycle" keyword, too. There is a high chance that you will find some dead shrimp in the next few days and/or weeks.

[Lukes Shrimp]

I forgot to mention I got the tank from someone else before and it was already cycled. I got the tank with the shrimp, gravel, plants, and half of the water. I Filled the rest of it with pure reverse osmosis water.

[Mustafa]

Go get a pH and kh test kit. Let us know the results. You don't usually want to fill up a tank with RO water. If the other half of the tank was already filled with very low pH water, you may have caused a pH crash. Dechlorinated tap water is the way to go. If your tap water kh is above 3 then you can mix in some RO water with tap water to achieve the desired kh in your change water. Never use pure RO water.