Nitrate does not directly kill or cause disease like ammonia or nitrites. However, it is still something to not be taken lightly. Nitrite is converted to nitrate by bacteria in the final stage of the nitrogen cycle, which can used by plants and algae as food. It is a nitrogen atom with three oxygen atoms attached to it.
It is not dangerous short term, but can lead to many severe complications if not treated properly. For planted tanks because the nitrogen cycle does require a certain amount of nitrates present in your water it is okey to keep it at about 15PPM. For an unplanted tank 5PPM, although as close to 0PPM is the ideal. Extreme levels such as 100PPM will decrease the amount of oxygen in your tank by a significant amount, and cause stress in your tank mates.
Imagine how hard life would be and how stressed out you would be having to go though your day having a hard time breathing. You would get stressed out pretty fast too, and everything you do would probably feel like its ten times more difficult to do – because your body needs a sufficient amount of oxygen as fuel for your muscles and organs to function properly.
High stress can cause many complications in shrimp just like it does in any species. Have you ever been in a high stress situation for a long time? It escalates to the point that when it seems the most inconvenient or the worst possible time, you end up catching a cold, or getting sick in some way? This is no coincidence. Stress puts the body in such a state that causes, higher blood pressure, physical pain, digestive problems, disruptive breathing and sleep and overall a lowering of immune system which makes you more prone to viruses. If prolonged long and severe enough it can even be linked to heart attacks, strokes and cancer. Basically stress causes the body to slowly self-destruct and it is the same for your aquarium shrimp and fish.
Stress makes their organs work harder, and hinders the ability to fight disease, and to heal itself. This makes the shrimp or fish harder to adjust to fluctuations in your water quality as well as hinder their ability to reproduce. This is why Nitrate is something not to be taken lightly. It can change the water chemistry in your tank causing a serious algae outbreak, so if your shrimp appear sluggish and have no appetite and you notice a lot of algae growth in your tank then it is probably due to high Nitrate levels.
Many things can cause persistent high nitrate levels such as over population, overfeeding and the presence of organic waste or a high amount decomposing plants and algae in your tank. This waste can be buried deep in fine sand, under rocks and gravel and be hiding in your canister filters.
Make sure that you check your Nitrate levels regularly, and do water changes regularly to keep your nitrates in check. Keep your plants well maintained and always trim off visible decomposing leaves if possible. If your nitrate levels have a hard time decreasing, you may want to use a substrate vacuum on your substrate or sand to get all the decomposing matter out that may be hiding there, as well as thoroughly cleaning your filters and changing your medium. A happy shrimp is a healthy shrimp -In the case of Nitrates, this is definitely true.