Hydrogen Sulphide (2)

Hydrogen Sulphide

Toxic hydrogen sulphide is a silent killer that often goes unidentified as the real cause of fatalities or sick pond fish. Never disturb a biological filter bed without rinsing and flushing the chamber. Beware of walking on an in-pond gravel filter bed!



Sulphur is excreted in the form of sulphide by certain bacteria under anaerobic conditions. Pond bottoms, filter bottoms and other areas where organic wastes settle are particularly prone to sulphide production. These sulphides present themselves in different forms in water. The lower the pH and the lower the temperature, the more hydrogen sulphide will be in solution.

Hydrogen sulphide is extremely toxic for fish particularly when present in the pH range 5,0 to 8,0 where it will interfere with respiration at cellular level to cause symptoms of hypoxia (oxygen shortage). The fish will increase their ventilation rate and become more active in an effort to find an escape route from the toxic environment. The toxicity increases with decreasing DO concentrations. It is lethal to adult fish exposed to 0,04 mg/l. Consider any detectable concentration of hydrogen sulphide to be detrimental to fish health in the long term.

Good pond hygiene and regular maintenance will eliminate the chance of hydrogen sulphide accumulation. Any disturbance of the biological filter bed should be flushed away immediately. Sand filters that are backwashed, should be rinsed properly. Flush the bottom drains regularly and remove uneaten food, excrement and dead organic material. Clean the filters at least twice a year. Regularly remove all sludge buildup.32, 33, 34, 35

Other than a major water change and vigorous aeration of the pond is about all you can do to solve the problem of hydrogen sulphide poisoning. The oxygen in the air oxidises the sulphide into harmless sulphate.

The formation of hydrogen sulphide will be limited or even prevented by running the pond at a higher pH (7.5-8.3) and with sufficient calcium ions in solution. This can easily be achieved by operating the pond water system with sufficient StabHi pH Pebbles in place.


(Extracted from Living Jewels (1996) by Ronnie Watt and Servaas de Kock, updated 2004, 2018.)

Reference material sited:
32. Boyd, C.E., 1990
Water Quality in Ponds for Aquaculture
Birmingham Publishing Co.

33. Boyd, C.E., 1982
Water Quality Management for Pond Fish Culture
Elsevier Scientific Publishing Company.

34. De Kock, S., 1994, 2017
Personal observation.

35. Yamada, R., in Lannan, J.E.; Smitherman, R.O. and Tchobanoglous, G. (Editors), 1986
Principles and Practises of Pond Aquaculture
Oregon State University Press