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Re: NO3 and PO4 in Takashi Amano Aquaria

John Fitch wrote:

There are two further measurements given [in Takashi Amano's TAG article], which I hope someone will
explain. They are TH of 20-40 mg/l and COD of 4-6 mg/l. Thanks.

Hey John,

I suspect TH = total hardness. COD = chemical oxygen demand. It's defined as the amount of O2 required to oxidize both inert and bio-available organic compounds into CO2 and water. The decomposition process uses up dissolved oxygen (DO) that fish and other animals need, so I assume that Amano-san uses COD as a measure of water quality (lower = cleaner), but he may have other motives.
Chuck Huffine
Knoxville, Tennessee