Hi, I added 4 Yoyo loaches to an established 55 gallon tank, 0 ammonia, 0 nitrite, 20 nitrates., temp 26.C, pH 6.4 yesterday and so far 3 have died. They have no signs of anything on their body, they just lay at the bottom and weren’t able to move until they stopped breathing. I also added cherry barbs but they did not die. They were acclimated before adding.