Hi @Taylor,
This is seriously shooting from the hip, but you sound like you need help ASAP:
Based on the death rate, it might not be viral. ( unless you added new shrimp in the last 2 weeks?)
we are assuming you have not added any decor, new ferts etc to the tanks.
Your tank has been running over a year, so it might be bacterial, due to imbalance in the ecosystem, based on your death rates.
Have you looked at the shrimp carefully to see if anyone is showing signs of illness? In the infection and disease guide they usually show the obvious ones, but not the subtle diseases...The dark organs behind the eyes ( small one on top of head is the stomach, but the fleshy brown-red largest organ is the hepatopancreas). If you have some of the RCS with lower quality colour, you can have a look at the hepatopancreas through the shell: light pink to yellow is sign of infection, usually bacteria. If some of the shrimp have a slight colour loss and slight/small white spots throughout the shell, it might be Microsporidium/Myxosporidium ( I am trying to identify this but it is extremely hard and this is speculation at this stage based on experience)- in this case the shrimp might appear normal and have foraging eating behaviour, but it is easy to spot the affected shrimp as they 'forage' like zombies in the same spot without moving at all for at least 5-10 minutes. Can you see the intestine/ digestive tract through the shells? If so, is it filled with waste or is it empty?- a good way to check if a shrimp is ill.
Do you have measures for controlling accumulation of organic wastes in your tank? You cannot measure this with TDS: you might need to do a thorough substrate vac without stirring up organic waste into the water column.
I would highly recommend doing a thorough gravel-vac with a water change and adding Dr Tim's Eco-Balance probiotic( freshwater one) at full dose to outcompete potential pathogens. There is anecdotal evidence on Quorum -sensing that might shut down pathogens or just outcompete them for nutrients and territory. Regular bacterial supplements for shrimps won't help in this case as they grow/divide to slowly- you need a probiotic to outcompete pathogens fast if you potentially have a bacterial outbreak.
If you manage to identify sick shrimp, isolate them immediately. Treating shrimp is risky and once a shrimp exhibits symptoms their fate is usually sealed, but there are treatment options mostly once we know more of what you are dealing with.