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Sudden Fish Deaths

Question: My tank was going great until I cleaned my filter, now my fish are dying, what have I done wrong?

Answer:  Over cleaning of the filter system or the addition off excessive amounts of Chlorinated water can adversely affect the Bacteria in the Biological filter.  As a result, Ammonia or Nitrite levels can rise sharply. 

Most people never think of their filter system as a living organism, but in reality that's exactly what it is, and just as sensitive as any other creature in the tank.  Extremes of temperature or water chemistry can have a devastating effect on the Bacteria which process the dissolved toxins in the aquarium.

The best course of action is to reduce feeding and carry out small frequent water changes, 5% - 10% daily until things return to normal.

Question: I bought new fish and next morning they are all dead. My old fish are OK!, so the new fish must have been diseased, right?

Answer: Wrong.! The most likely cause is low pH in your tank. The pH in an aquarium falls slowly over time and your existing fish adapt, they may not like it, but they do adapt. However, new fish, no matter where they were purchased, will be in water pH => 7.0, and the sudden change causes shock resulting in death in a few hours.

This is probably the most compelling reason for regular weekly partial water changes. While some species do like a low ph, most don't, and NONE will tolerate a sudden change. Here in Northern Ireland our tap water is of medium hardness with a pH 7.2 - 7.4

Maroon Clownfish in an Anemone