As already mentioned earlier I tested some NH4 (0.6ppm) and my Amano shrimps were obviously under stress (not eating just hanging on one spot).
I started dosing Easy Life FFM (fluid filter medium) and just half an hour after dosing it the shrimps started behaving normally (eating, foraging).
This product probably contains liquid Zeolite which has a very good CEC (cation exchange capacity) which had removed the NH4.
Now I dose this product to all my tanks instead of the Tetra Aqua Safe.
Read more about Easy Life FFM here