Question of the Day

Ask: Did you use chlorine or other chemicals near the tank/equipment or do a recent water change with tap water? Chlorine is commonly used to disinfect tanks and equipment but is highly toxic to fish. This is a common problem because both chlorine and chloramine (type of chlorine stabilized by amination) are frequently found in municipal water sources.

Chronic and subacute chlorine exposure result in signs as described here: cloudy eyes, inflammation and necrosis of the gills, excess mucus covering gills, and lethargy. Acute chlorine toxicosis can cause sudden death.

There is a colorimetric test readily available from pool supply stores that measures chlorine (free and total); levels should be nondetectable when tested on site. If the sample of water needs to be transported for testing, use a sealed glass bottle with no air space (it may dissipate); false negatives are possible. Need to measure both free and total to get the most accurate results.

Tx with dechlorination products (often containing sodium thiosulfate) available at pet stores and then recheck free and total chlorine levels. Increase aeration because of gill compromise. Addition of 1-3 ppt salt may also help with osmoregulatory issues.

Check out this article on “Emergency Care of A Tancho Koi (Cyprinus carpio) Suffering From Acute Chlorine Toxicity” by Bakal et al. from North Carolina State University.