I had 8 Rummynose and 1 angelfish in a 37 gallon tank. The tank has been cycling for 4 weeks and water levels are 0,0 Ammonia and Nitrite, 10 Nitrate, 7.4 Ph. The angelfish was just added a couple days ago since I was getting no ammonia for a week. I have a sun sun 304 that I set up about 1-2 weeks ago. It has the old filters media inside plus lots more. I came home today and all of my alive fish were at the surface gasping for air. 4 rummy noses were dead. The water temp was 81 F. Was there no oxygen in the tank? I immediately added an air pump and wondering what else I should do. Please help I dont want to lose all of my fish.