David0121: your readings are not fine. Nitrites over 0.25 ppm are too high. You are well past due for a large water change. I would do no less than 50% if you want to slow the fish deaths.
Loui354, please read up on fish-in cycling here on our site. A reading of 0.3 ppm nitrite is not a mere detail, it is the essence of being too high.
Loui354, please read up on fish-in cycling here on our site. A reading of 0.3 ppm nitrite is not a mere detail, it is the essence of being too high.

0.3 Less Than 3