A Magic Ratio? Nitrate & Phosphate Ration vs Concentration

Is there a magic ratio? There is a perfect balance between nitrate and phosphate, regardless of whether the actual levels are elevated. If we maintain that excellent ratio to each other, the corals thrive, it is the answer to Algae, Dyno, Cyanobacteria, and nutrients in our reef tank.

The conversation has evolved from just concentration or parts per million of nitrate or phosphate in the tank to maybe something different like the ratio, especially in relation to what happens when one of these things is limited and the other is abundant. What types of organisms grow in this environment. The answer to this question is we don’t have all the answers. 

But there is one thing that is true for sure: evolution will be found in the desire to find out.

The Proofs from Oceans

It has been pretty well documented in the ocean that when nitrogen or phosphorous is either elevated or depleted individually or at extreme ends of the ratio, it often increases the likelihood of pests overtaking the area. The same is true for our aquariums.

A big portion of this conversation is over 0-years old with the Redfield ratio. Alfred Redfield discovered that the percentage of Nitrogen to Phosphorus is a reasonably consistent 16:1, i.e., for every one part of phosphorous, there are 16 parts of Nitrogen throughout the world’s ocean.

They don’t resolve nutrients like Nitrate and phosphate, but the biomass of collected phytoplankton in organic nutrients in the ocean all 16:1.

You can convert that 16:1 nitrogen to phosphorus, nitrate, and phosphate, which we commonly test for. Ideally, it is NO3:PO3 = 10:1. So, there will be ten parts per million nitrate for everyone part per million phosphates.

Now, the big question is, is that 10:1 nitrate to phosphate is just a happy accident and where the ocean just landed and tends to thrive, or is it a ratio—more than just a specific number that travels up and down has predictable results in our aquariums.

There are the questions we are tempted to answer.

Let’s Find the Answers

There is a slew of resources, websites, and calculators dedicated to some of these ratios. They will tell you what they believe will happen when you deviate from them. Not just at the low end but also at the high end, and which organisms are more likely to thrive in those environments.

Understanding that phrase is more likely is important because you have not created any certainty of anything, just an increase of chances by creating an environment of nitrogen and phosphorous optimal for some organisms.

The closer you get to the optimal range for that organism and the further you get from another, increasing the chances of that happening, but not a certainty, just an increase in the chances.

Though most photosynthetic organisms indeed have a preferred ratio of nitrate to phosphate, they thrive when you meet it. You can see that ratio listed on the side of almost every plant fertilizer; some ratios are better for different plant stages of root production, leave growth, and flowering or fruiting.

It is undeniable that different rations present different results with different organisms’ needs, some thrive, and others don’t.

This is most commonly observed at the extremes where there is no phosphate or phosphorus available in the tank. Still, there is an adequate or even elevated amount of nitrogen, nitrate, or the inverse.

In this case, some organisms will do very poorly, and some will thrive.

Now, this could be that we just created the optimal ratio for that specific organism, or it could just be that they are better equipped to scavenge in an environment where nitrogen or phosphorus is limited. But in either case, they are both competing for space now.

And most of us would like to see the Coraline algae, beneficial bacteria, or even corals win over the pests.

So, is it concentration or ratio? And if it is a ratio, does the effect of this scale infinitely up and infinitely down, or is one part per million nitrates in a tenth of parts per million phosphates which is a reasonably low concentration foin to produce the same results, or allow the same organisms to thrive as 10:1 ratio.

The Puzzled Answers

Both of these are 10:1, but with a different concentration, one high and one low, will the same organisms thrive in either environment even though the concentrations are different. The answer is probably not, but we don’t know that definitely, and it might be something entirely different.

There is not much data to look up to other than emulating seawater produces the highest percentage results. However, the further away from the natural seawater concentrations, the less likely the results will hold.

Probably the most under-appreciated piece in all of this is the fruit that we put in our tank. Some might be 5:1 to 40:1.