I have a 125 setup with fluval fx5 and hob filter... In the tank was 18" silver arawana (dead now), 2 18" tiger shovelnose, 2 12" oscars, 18" clown knife..and 18" pleco...did about 25% water change and had an ammonia spike...lost my arawana :( ..ever since I've checked perimeters and they are...