Hello, we finished building a koi pond in our backyard halfway through August, we filled it with tap water and used Aquascape Detoxifier. I waited about 2 weeks to put fish in there because my tap water had a 3 ppm of nitrite(according to Tetra test strips). I didn't quite believe this so I went ahead and got the Seachem MultiTest Nitrite & Nitrate. This test said that my tap water had a .25 PPM of nitrite. I also added the Aquascape starting bacteria before adding my koi. When I added the koi I didn't have much of an ammonia spike because I was using the Aquascape Detoxifier to lower the level of free ammonia. Last week nitrite started to show, however it was barely noticeable (>.01 PPM) Then suddenly the nitrite rose to .5, when this happened I started adding salt (Morton Blue Bag Salt). Throughout the past few days the nitrite reading is around 5 ppm and sometimes higher. I have my salinity level to .15%, I've doing 13% water changes. I treat the water with the aquascape detoxifier and also add enough salt to bring it to .15% before adding it to my main pond. However the water changes don't seem to be doing much, the nitrite still really high (Around 5ppm and sometimes higher). I haven't seen my fish going up on the surface to gasp like I've read that some do when they get brown blood disease. My tank is about 1400 gallons (8 ft x 10 ft x 5 ft deep). I have 5 koi(2-12",1-11", 2-9"). As of right of now one of the 12" inch koi is not in the main pond, he is in the quarantine tank due to a head injury. I would appreciate if someone could help me out, I'm new to this and I can't seem to figure out how to lower the nitrite levels to a more acceptable levels. Thank you