I stocked my 75 gallon tank about 2 weeks ago with white labs, red zebras, yellow tail acei, and cynotilapia zebroides lundo reef. The yellow tail acei and red zebras are all about 2 inches long the white labs and cynotilapia are 1.25 to 1.5 inches. 6 days after stocking one of the cynotilapia suddenly died. I looked over and he was just floating dead. Since then I have lost more fish 1 every day or 2. It first it was only the cynotilapia that were dying but now one of the white labs have died too. Most of them I have found dead when I get home from work. They will be mostly eaten by the time I get them out. I started treating with api general cure on Wednesday. I haven't seen any overt attacking or damage being done. I'm really at a loss to what the problem is. 0 ammonia 0 nitrite 5 nitrate 7.2ph. I know the ph is not ideal but I figured they would adapt. The tank is aquascaped with flagstone from a local landscape yard. Any help would be appreciated.