Hey guys. I’ve started cycling my tank 3 weeks ago. Followed Brightwell ammonium dosage for my 280 gallons. I made a mistake of listening to some YouTuber saying u dun need to test nitrite and as long as ammonia is 0 and nitrate is detectable. Ur good to go. What happens next is I went ahead to add 15 fishes and next morning 3 died. 1-2 was gasping for air. I suspect it is high nitrite and went ahead to get a nitrite test kit and found out that my nitrite is above 5 ppm. I stop feeding and dose Seachem prime, which seems to stabilised the fishes. Did a 50 pct water change today and tested my nitrite, it dropped to 0.5 ppm but within 5 hours I did another test it was back to 2-5 ppm again. What else can I do to help this situation?