I lost the first discus last night, starting the tetracycline today, how long should I leave it in the tank before doing another water change, it doesn't state on the directions for use, I am guessing 7days. PH 7.1, ammonia .1 ppm, nitrite 0, nitrate 10 ppm, I have vacuumed the gravel and added another 9500 dual air pump while the tetracycline is in the tank.