I am using air pump and air stone for adding O2 to the tank, i am not running CO2.
I am using Tetra test set. They are somewhat difficult to read sometimes, when i was testing for ammnium i am comparing the color of the test to be close to zero. But this might be enough to kill shrimps.
The label for the soil i used for this tank has this text:
Quality Soil particularly suitable for indoor plants and window boxes. Nutritious and odorless. The earth is long time composted in 3 years, and are hand-pruned several times during this period.[censored]The result is a nutrient-rich soil full of microlife, ideal for your indoor plants and window boxes.[censored]Debio Approved for organic growers. Raw materials: 30% cow manure, 60% peat and 10% sand.
The tank the shrimps are in no is also a low tech tank with soil, but it is a different soil with no added fertilizer. I have only done top of on this tank, never waterchanges, the shrimps still thrive in this tank??
Here are some pictures of the two tanks, the first two pictures is of the tank that kill shrimps:
Soil test pictures
if they are getting bad so fast and getting better so fast try adding more o2 to the tank, your not running co2 are you? some thing is not right as the only time i have seen shrimp act like that and then get better is form lack of o2. what soil did you use? do you have a lot of bubbles coming out your soil? and what test kits are you using?