Question regarding the ratio of nitrates to phosphates

[awestruck]

I hope no one here becomes angry about this question because it is in reference to a freshwater planted tank. This is the best chemistry forum I know of so I thought maybe someone here could answer this.

A freshwater planted tank seems to flourish if the nitratehosphate ratio is about 10:1 (at least this is what I've been told by several people). By flourish I mean that the plants are growing nicely and are not getting any algae on them.

Because I have a higher light output I am dosing carbon daily. The photoperiod is only 7-8 hours which is recommended for FW planted tanks. And, there is a slow flow which creates a gentle flowing of the plants, but not enough surface turbulence to drive down the co2.

Ok, so back to the NO4O4 ratio. Can anyone even hazard a guess as to why this seems to be the range that encourages healthy plant growth yet discourages algae growth?

 

[HighlandReefer]

What most hobbyists refer to regarding the ratio of nitrogen to phosphate that is utilized is the Redfield Ratio which states:

The molar elemental ratio C:N in most phytoplankton is 106:16:1.

This Redfield Ratio represents an average of all phytoplankton, so some may utilize these elements at different ratios. Each algae or other organisms may be different.


"Can anyone even hazard a guess as to why this seems to be the range that encourages healthy plant growth yet discourages algae growth?"

Some algae are easier to control keeping your water parameters correct. Others are not easily controlled by maintaining correct water parameters. If there is adequate nitrogen and phosphorous available & let's say you have high iron levels, then algae can grow very rapidly given this scenario & so can aquatic macro-algae and plants.

In the natural, pristine, ocean reefs, phosphate is the limiting factor in most cases. PHosphate levels there are only at 0.005 ppm which is well below what our test kits can detect. Given this amount of phosphate, then nitrate would only need to be at 0.05 ppm to maintain adequate growth for many stubborn hard to control algae. Our test kits can't detect nitrate at those levels. SPS Coral need this level to survive as well. If this is the case, your not going to control these algae without resorting the mechanical removal or perhaps AlgaeFix if it kills that specie of algae.

Keep in mind that fish food is the highest source of both phosphate and nitrates. Overfeeding fish results in excess phosphate and nitrate being excreted as wasts.

 

[jdegrasse]

So I can only answer in broad terms. It is about limiting nutrients.

The Total nitrate:Total phosphate ratio (TN:TP) has been measured in various bodies of water. The goal of the research is to measure the effect of nitrate and phosphate in our waterways.

The overall data shows that algal growth is limited when the ratio is ~10:1. (That's a gross oversimplification, but apparently it works for a planted tank.) When there are blooms, the ratio tends to be higher (>20:1).

The explanation for this observation is that at that ratio, the nutrients (N or P) needed for to start and sustain an algae bloom is severely limited.

Plants are a different story. From a TN:TP ratio of 5:1 to 10:1 they are not nutrient limited. But outside this range, they are nutrient limited.

Why plants and algae thrive in different TN/TP ratios is due to a fundamental difference between the biology of Tracheophytes and Thallophytes.

If you want more detail, google "TN/TP" along with algae or plants -- tons of information about the biology.

 

[awestruck]

Bless your heart for answering!

Ok, I'm using dechlorinated tapwater, nitrates measure 5. I don't know what the phospates are at. I was told that in addition to carbon and trace elements, I should add iron, a nitrate fert. and a phos. fert. I'm only experiencing some small algae on the plants, and interestingly only on some of the plants. Truthfully it looks like diatoms (tank is only 8 weeks old).

It sounds like you're saying to eliminate nitrates and phosphates? I'm sorry, maybe I didn't read it correctly. Plants need nitrates and phosphates (from what I'm told) which seems so contradictory because phosphates feed algae.

 

[awestruck]

So I can only answer in broad terms. It is about limiting nutrients.

The Total nitrate:Total phosphate ratio (TN:TP) has been measured in various bodies of water. The goal of the research is to measure the effect of nitrate and phosphate in our waterways.

The overall data shows that algal growth is limited when the ratio is ~10:1. (That's a gross oversimplification, but apparently it works for a planted tank.) When there are blooms, the ratio tends to be higher (>20:1).

The explanation for this observation is that at that ratio, the nutrients (N or P) needed for to start and sustain an algae bloom is severely limited.

Plants are a different story. From a TN:TP ratio of 5:1 to 10:1 they are not nutrient limited. But outside this range, they are nutrient limited.

Why plants and algae thrive in different TN/TP ratios is due to a fundamental difference between the biology of Tracheophytes and Thallophytes.

If you want more detail, google "TN/TP" along with algae or plants -- tons of information about the biology.

Bless your heart as well.

So, again if I'm reading this correctly, basically my nitrates are actually not high enough in relation to the phosphates? If this is the case then I should add nitrate fertilizer but not phosphate fertilizer.

 

[awestruck]

I feel a headache coming on.

 

[jdegrasse]

I would add fertilizer so that the ratio of n to p is about 10:1. But you have to measure the phosphates in order to know what your tanks ratio actually is.

 

[awestruck]

I would add fertilizer so that the ratio of n to p is about 10:1. But you have to measure the phosphates in order to know what your tanks ratio actually is.

Thank you so much. To reiterate, I belong to reef central but also started a little freshwater planted tank (it's very pretty btw ). This truly is the best chemistry forum I know of so asking here made sense.

I will test the phosphates today because I don't want to dose anything till I know where the water is at.

 

[jdegrasse]

Good luck!

 

[awestruck]

Thank you. I haven't killed anything yet so I guess that's a good sign.

 

[dixiedog]

I feel a headache coming on.

I've found liquor helps with that.