Extremely high nitrates - how do fish live?

[SchizotypalVamp]

Also remember that some fish are more sensitive to nitrates than others. Some can tolerate exceedingly high amounts and be fine, and others will not.

 

[KarlTh]

Most fish only show life-threatening reactions to nitrate in the 1000ppm upwards range. Negative reactions at lower levels, yes, but not necessarily fatal. Other fish are indeed acutely sensitive.

 

[Woofy]

When i moved that i had to leave my tanks behind for a while checking on them back and forth i actually had the water test for ammonia once come back dark blue....i have no idea what dark blue meant but it couldnt have been good yet not one death and most of the fish are still alive and well in our 125g. Yet i have had the problem when leaving a tank with poor water quality then suddenly changing it that fish die from the sudden change. EEK! so change the water slooowly back to health.

 

[THE V]

How severely the nitrate effects the fish is dependent upon the pH and the buffering capacity of the water. The toxicity of nitrate is from suffocating the fish by bonding to the hemoglobin in the blood. In order to get enough oxygen the fish has to increase the amount of hemoglobin in its blood. If the nitrate builds up slowly the fish doesn't have that much problem adjusting.. for a time. Eventually it reaches a limit and most of the fish will die at once. Depending on the stocking level, the pH and the buffering capacity, this can happen in a few months or it may take years.

The reason that changing too much water at once in this type of tank is dangerous is different. When people do not change the water (only top off) the level of all types of ions in the water builds up. As the ions build up the fish's kidneys have to expel less and less water (look up osmosis and diffusion if you want to understand why). With the kidneys not moving as much water, cellular waste can build up. Or more simply the fish is dehydrated (prolonged dehydration can also lead to death). When some sympathetic person changes too much of the water, the radical change in ionic concentration can cause the fish to hyperhydrate. Basically, they die from having too much water in their cells (drink themselves to death). So slower, smaller water changes are required.

 

[wataugachicken]

Fish do this in the same way the addicted expose themselves to doses of various drugs that would easily kill a non-user. They slowly build up a tolerance.

As you clean up the tank, vacuum a little section of substrate gently, but thoroughly each change, avoiding setting any toxic pockets loose into the tank water.

that's a good way to put it. also allows for OTS/big water changes to mimic dangerous withdrawal effects from going 'cold turkey'.