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Copper Sulfate (Crystal Blue) product killed my Koi. What now

Q. I was sold a product called crystal blue for controlling algae in my Koi pond. I had a total fish kill over night. Does the product totally dissolve in the water or does it leave some undissolved residue. I have reintroduced fish twice and have experienced a fish kill each time. Is my only solution to drain and somehow wash out the pond?

J.B. west
- Ft Worth Texas

simultaneous 2005

A. You picked about the fastest and surest fish poison that exists, to put into your tank. Drain, flush, drain, flush, and so on until copper concentration is down to parts per billion, and then fish will not be poisoned.

Bill Reynolds
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.


A. If the copper concentration killed the first fish, why would you not expect it to kill the fish each time afterwards?
It strongly appears that you either did not weigh properly or you miscalculated the total gallons of water.

Drain it and flush it several times and start over.

James Watts
- Navarre, Florida


A. I had a similar occurrence with my fresh water tropical fish. One of the dead fish was at least 15 years old! I also have a pond in my garden that is very prone to algae and I find the best natural treatment is to use barley hay. Stuff a pair of your wife's tights with the barley hay and throw it into the water (preferably without her in the tights!). After a few days the hay will start to sink and as it does, it clears the pond water. I would suggest you tie a chord to the tights so you can get them out again. Leave it in the pond for the whole season and replace it as needed. Over here they are now selling concentrated barley hay extract, but I have never used it. I prefer the natural stuff as it offers nutrients to the plants as well as killing the algae. Be warned, you must use barley hay, nothing else works. I would also suggest it is one that is not treated with any artificial chemicals such as pesticides.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

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