Stress gives us headaches, makes us feel lousy, tears down our systems and causes heart attacks that can lead to death. We often ignore the warning signals and will live many years under stress. The affects of stress is even more apparent in fish than in humans. It's stressful for them to eat and to spawn. If the pH is off, if ammonia, nitrites or high concentrations of nitrates are present in their water the fish will stress.
Stress leads to all the other afflictions that can occur.
Parasites and Aeromonas must know how to read because it is when the fish is at its most vulnerable condition that these bad elements tend to attack. Parasites and bad bacterias are present in ponds. The trick is to offer the most stress-free environment for your fish so that they can live healthfully. Your fish suffer when the water parameters are not stable. Any reading of Ammonia or Nitrites, even mild readings, and swings in the pH will cause stress.