Redfield Ratio

What is it?

The Redfield ratio is named after Alfred C. Redfield, who first described the ratio in an article in 1934. In 1934 Alfred Redfield analysed thousands of samples of marine biomass from all ocean regions. He found that globally the elemental composition of marine organic matter (dead and living) was remarkably constant. The ratios of carbon to nitrogen to phophorus remained the same from coastal to open ocean regions. The elemental ratios he found were:

C:N:P (Carbon, Nitrogen and Phosphate) as 106:16:1. This is known collectively as the Redfield-Richards Ratio.

It is used in aquariums to calculate and so help eliminate algae from freshwater or salt water aquariums.

Redfield Ratio

Phosphate mg/l	Nitrate
	0.01	1	2.5	5	7.5	10	15	20	30	40	50
0.01	2	153	383	765	1148	1530	2295	3060	4590	6120	7650
0.05	0	31	77	153	230	306	459	612	918	1224	1530
0.1	0	15	38	77	115	153	230	306	459	612	765
0.2	0	8	19	38	57	77	115	153	230	306	383
0.3	0	5	13	26	38	51	77	102	153	204	255
0.5	0	3	8	15	23	31	46	61	92	122	153
1	0	2	4	8	11	15	23	31	46	61	77
1.5|	0	1	3	5	8	10	15	20	31	41	51
2	0	1	2	4	6	8	11	15	23	31	38

So measure the Nitrate and Phosphate levels and using the chart see where they meet.

When the ratio is below 10 there is a likelihood of blue-green algae forming When the ratio is above 22 there is a likelihood of green algae forming

Links

• Free of algae with Redfield ratio with chart
• Redfield ratio and Algae control