I do 25% water changes once a week in all of my tanks, its also very important for you to use a dechlorinator such as Seachem Prime when the source of the water is from the tap, even when you know there is no chlorine in your tap water there is nothing to stop your water company flushing the pipes with any type of chemical, normally they do this when there is storm damage and pipes get broken.
In some of my tanks I change 50% of the water every week so what I need you to understand is water change size depend on your ability to measure your own waters makeup and keep it stable to what your shrimp are used to.
Let me give you an example
Water direct from the tap no prime used 5% water change done because a guy on YouTube said so.
RESULT molting issues from unknown water makeup, deaths from high fluctuating PH..Unknown chemicals introduced..
50 % water change done with aged reverse osmosis water to a TDS of 150ppm
Result lots of babies and breeding.
I hope you see the difference, learning to deal with water is the key to shrimp keeping.
Notes on reverse osmosis
Change your filters every 3-4 months the large membrane can last up to 3 years if you protect it properly. I like to double up on my carbon filter and switch one out every 3 months to be super safe, also write the date on your filters so you know when to change them.
Flow rate back into the tank is also water make up dependent, if you are not sure on what you are doing or use tap water then slower is better you want to drip your water back into the tank at a rate of around 2-3 drops per second.
The Reverse Osmosis I use I add back in at a rate of a few liters a minute. the reason for doing water changes is simple you need to chuck out waste and replace it with fresh water and minerals, these will help your plants bacteria and shrimp grow