Salt how much/how long is enough

[Simi Koi]

I routinly use salt when I test Nitrites. I am always receiving new shipments of koi and will clean out the empty QT with 3-4 ppm of PP before the new fish go in. The bacteria dies off a bit after this treatment and I get a spike in ammonia then in nitrites for the first couple of weeks. I will usually keep the salt at .3% until the nitrites cycle out. but is there a suggested salt % per ppm of Nitrites?

[kingkong]

My favorite word. Salt can reduce the toxic effects on an interum measure until your bio-convertor can catch up with added load of fish. Free ammonia is the most toxic followed by nitrites. Just one thing to understand why the "salt" is added so that the more desireable salt is used if possible.
"Salt" improves the gill function by helping maintain a natural balance of electrolytes in the body fluids. This balance of electrolytes is essential for oxygen uptake and release of carbon dioxide and ammonia. Now, electrolytes are not just sodium chloride (table salt), but comprise of pottassium, sodium, chloride, calcium and magnesium to name the majors. Sea salt has all the necessary electrolyte elements so osmotic shock can be temporarily blocked during nitrite and ammonia spikes.
This is one calculation I saw;
Nitrite levels at 1 ppm 1 lb. per 100 gal
1 -2 ppm 2lbs per 100
2-4 ppm 3lbs per 100
4 ppm or greater transfer to new water
More to the point;
Nitrites actively transported across gills oxidizes hemoglobin to form methemoglobin which can cause sudden death. Adding the specific chloride ion competes with the nitrite ion to be transported across the gills. The Chloide ion has to be at least 3 times the level of the Nitrite ion and no more than 7 times. With this method of blocking, chloride is the only element active or necessary.

[Russell Peters]

As well as adding salt, we will routinely add KI nitrifier to boost the lost bacteria.
The net result is usually no nitrites in a day, maybe two.