Mine in Rochester, NY was too a 40 gal. 40 gal of 140 F water (highest) plus 45 F incoming water should make about 150 gal of 80 F water. I'd use a stove, etc. too. They may not last a few days with such high nitrites. Just trying to help. I am sure you know what you are doing.
Are there things for nitrites analogous to ammo-lock for ammonia?