Nitrate Level

[Ch4rlie]

I have always been a believer of having nitrate in the tank, mainly for plants more than anything and always maintained that nitrate at 60ppm should be fine as longs not long term, and doing weekly water changes and plants consuming nitrate was the best way of controlling these levels.
 
Did once have nitrate shoot up to 160ppm (tested 3 times to be sure!) for unknown reasons and not sure how long for, less than a week for certain though, and appears to have no ill effects on my threadfins, RCS and assassins I had at the time.
 
So, imho, having a average of 10 to 40ppm of nitrate for the tank and fish and shrimps always seems to be comfortable with this level, I never worry too much about nitrate.
 
As for sugars in plants or anything like that, sorry, no idea about that sort of thing, but the theories that have been said already do sound kind of plausible, not something i know about so best not to comment on that

 

[TwoTankAmin]

While I do  keep planted tanks and have done some research into a bit of the aquatic plant world, it is more curiosity that motivates me rather than trying to make sense of it all. I do know that certain plants will actively transport oxygen to their roots and release it in order to help bacteria colonize the area. I know nothing about sugars and lack of nutrients.
 
But using what little common sense I still have, here is what I wonder. Algae uses many of the same things that plants do- ammonia, light, co2 etc. So how is it possible in a tank with both plants and algae to deprive plants of nutrients and not be doing so for the algae as well? We also know that one way to battle bad algae is a tank blackout. We deprive everything of light and we stop adding ferts during the blackout. So the only food available is what the fish and organic degradation make. At the end of the week, when we lift the blackout, hopefully the plants are OK and the algae has been starved. The plants weather poor light and lack of nutrients better than the algae. So if we starve the plants in a tank of nutrients are we not also starving the algae and if so should not the algae starve before the plants? So even if it is correct that starved plant eventually release sugars, how would this benefit dead algae?
 
Incidentally. in looking for information on thisIi ran across other information showing there are now genetically modified algae that can produce biodiesel living in total darkness. But these are not natural, they have been engineered by inserting genes they do not normally have.
 
Finally, my limited understanding re algae in fw is that it makes its own needed sugars photsynthetically using carbohydrates and carbon:
 

 
Chlorophyll is like a factory within algae and is used to make its own sugars. These sugars are called glucose. All algae cells contain chlorophyll. Algae also need carbon dioxide to make
sugars............
 
The process of how algae make energy from the sun is called “ Photosynethesis”. It is like cooking, the main ingredients that algae need to make their energy and give us oxygen are:
Sunlight + Chlorophyll (in their cells) + Carbon Dioxide + Water = Glucose + Oxygen.

from http/www.biomara.org/schools/Lesson%202%20-%20how%20algae%20grow.pdf
 
 
Next, I apologize for the post above as in editing it one line ended up in the wrong place. The line after the first quote which reads
"Bear in mind that you need to convert NO3 mg/l-nitrogen to the scale used on hobby tests like the API kit you must multiply the nitrogen number by 4.4. So the above"
This should have appeared below the second quote so it read like this:
 
"Bear in mind that you need to convert NO3 mg/l-nitrogen to the scale used on hobby tests like the API kit you must multiply the nitrogen number by 4.4. So this means that, at the lowest value above of 191 mg/l-n which kills 1/2 the fish in 96 hours, 10% of this is 9.1 mg/l-n and would read 76.4 ppm on an API kit (assuming you got an accurate test result). That level is then considered safe and is a far cry from 10 or 20 ppm being harmful."
 
Basically, what science does is to ask what level kills 1/2 the fish when doing the research. However, what was also discovered was that at 10% of that fatal level, it is pretty much safe. Of course this is on a species by species basis. But that would eans the guppy fry in the study should be OK in nitrate that tests at 74 ppm on our hobby nitrate kits. My intent posting the information was to show that there is some research out there on species we actually keep in our tanks and that at least for the guppy)for example), nitrate levels can safely be much higher than those often stated in posts. At least that is what the paper I quoted indicates.
 
My point in all this is that all to often we see statements in posts about the level of nitrate, or how long the bacteria can survive etc. that get repeated over and over across general aquarium sites. The numbers are stated as fact without a shred of evidence that such numbers are actually valid. This is the sort of thing that got me started reading the research. What I found was there are lots of trained scientists and researchers who actually study these thing in labs under controlled conditions and a lot of this work is being peer reviewed for accuracy etc. There is a whole collection of information which is constantly subject to revision and improvement and even being completely replaced by new knowledge and research. But at least the research has some basis in science as opposed to being a repeated statement unaccompanied by any sort of support.

 

[daizeUK]

So how is it possible in a tank with both plants and algae to deprive plants of nutrients and not be doing so for the algae as well?

I reckon because algae and even different species of plants have different tolerances of nutrient levels and varying 'optimum' levels of nutrients.  I think algae requires much fewer nutrients than plants to operate efficiently.  I do know that plants can alter the mechanisms by which they process nutrients depending on how many are available, sort of re-programming themselves, however doing this uses energy and is stressful for the plant, which is why plants perform best when given high, stable levels of nutrients.  Algae are much more adaptable to fluctuating or low levels of nutrients.  
 
According to our Back to Basics planting article (http/www.fishforums.net/index.php?/topic/298133-back-to-basics/) :
 

First off can i just say Excess Nutrients don't cause algae. If you have any questions on this please ask as i can give out lots of information that shows otherwise. 

Nutrients feed algae, they do not cause algae.

And that is the important thing, and it is a big difference between cause & feed, that is where most of the confusion comes from. 
Algae is never CO2, or nutrient limited. Even the small amount of nutrients released by fish waste is enough for algae 

 there is no way around it. So using chemical removers means algae grows slower... it also means plants suffer.... which then means they leach ammonia and algae still has a source of nutrients 

Removing nutrients only makes problems worse, you need to address the cause, which is explained below under "algae"
 

 

[malfunction]

I might well have imagined it, but I'm sure I've read somewhere that having nitrates too low in your aquarium can be dangerous as it encourages the denitrifying bacteria to produce hydrogen sulphate.

 

[daizeUK]

I've never heard of nitrate levels having anything to do with that, perhaps you're thinking of anaerobic bacteria which can produce hydrogen sulphide gas in areas deprived of oxygen?

 

[TwoTankAmin]

Actually he is partly correct. Lets start with denitrification:
 

Biological denitrification is an anaerobic respiration reaction in which nitrate (NO3) is reduced. Denitrifying bacteria are aerobic autotrophs or heterotrophs that can switch to anaerobic growth when nitrate is used as an electron acceptor (Bitton 1994).  Denitrification can occur by two pathways.  The dissimilative nitrate reduction pathway requires anoxic conditions and results in the liberation of nitrogen gas from the water column (Reed et al. 1988; Madigan et al. 1997).  Under aerobic conditions denitrification results in the assimilative pathway or accumulation of nitrogen into biomass (Bitton 1994; Madigan et al. 1997).  It is desirable to encourage the dissimilative pathway of denitrification so that nitrogen may be completely removed from the system in gaseous form rather than simply recycled through the system in biomass.  In order for this to occur, there must be insufficient molecular or dissolved oxygen present so that the bacteria use the nitrate rather than the oxygen.  The rate of the denitrification reaction is relatively fast when there is no free oxygen present (< 0.5 mg/l is ideal).  The denitrification rate drops to zero when the dissolved oxygen level reaches 2.0 mg/l.

fromhttp/www.selba.org/EngTaster/Ecological/Water/Denitrification.html
 
Now if one has to much media designed to facilitate denitrification, it is possible to use up all the nitrate:
 

This denitrifier is now working too well and removing all the nitrates, which may force some bacteria to use sulfates and produce hydrogen sulfide........
The solution may be to remove some of the denitrifying media.....

from http/www.petfishtalk.com/shows_special/denitrification/denitrification.htm
 
Unlike much of the other bacteria in tanks, establishing denitrifiers takes many months, not weeks.

 

[daizeUK]

That's interesting.  Are the denitrifying bacteria the ones responsible for producing the hydrogen sulphide when deprived of nitrate or is it talking about two different species of bacteria?
 
It's commonly advised not to bank sand beds too deep due to the risks of anaerobic bacteria producing hydrogen sulphide gas - but is this saying that this will never occur as long as there is sufficient nitrate available?

 

[malfunction]

It's very slowly coming back to me... I came across this briefly when I was researching nitrate reactors, and wondering whether it would be worthwhile setting one up. As I understand it, the denitrifying bacteria can operate using both aerobic and anaerobic respiration. In anaerobic conditions where sufficient nitrate is present, they metabolise nitrate, producing nitrogen gas as a waste product. When both oxygen and nitrate are absent, they metabolise sulphur-based compounds and water, producing hydrogen sulphide as a byproduct. So theoretically, hydrogen sulphide production can be avoided in sand beds if nitrate levels in the water reaching the bacteria is above a critical level.

Having said that, I'm not sure if this process only occurs in nitrate reactors (where you deliberately provide sulphur-containing food for the bacteria) or if it can also occur in reactor-free aquariums. I only looked into it briefly so my understanding of the process is very limited.

 

[DaveA76]

thankyou for all the replies, now my head hurts 

 

[elmo666]

As I understand it nitrate is end product if the nitrogen cycle. An effective filter will produce nitrates so there's always going to be a detectable reading. Can't see how it can ever be zero, even in a heavily planted tank, as said plants require it as part of their nutritional requirements, so striving for a very low level is at odds with keeping healthy plants. A "safe" level is all very subjective to the individual set up and is dependent on so many variables any quoted figure is nothing more than a guess. What's often overlooked when algae problems arise ate phosphates and silicates which in my opinion have just as much impact, if not moreso as theses build up undetected in the tank, water changes add more if not passed over a suitable resin to remove them at source.

 

[TwoTankAmin]

There are several ways nitrate can be zero. As noted, nitrate is the end product of the nitrifying part of the cycle and denitrifying is the very end.
 
So how can one have 0 nitrates in a tank. Let me count the ways:
 
1. Low fish load means minimal nitrate might be created. The less there is, the easier various ways become to make it 0.
2. Lots of plants means two things. The plants use a lot of the ammonia (as ammonium) leaving little for the bacteria to convert to nitrate. The the plants use what little there is.
3. Mature tanks do not need anaerobic zones to denitrify, they need anoxic zones.
4. Anaerobic = total absence of free oxygen (O2) or bound oxygen (NO2, NO3). Anoxic = absence of free oxygen, but presence of bound oxygen. You get a different result if the is no oxygen in any form vs it being bound in nitrate which is one nitrogen and three oxygen.
5. #4 is why when one has denitrifcation capacity that having too much of it can use up all the bound O. When this happens the process becomes different and so does the end product. This is where the sulfur stuff comes in.
6. In planted tanks that have rooted plants in the substrate, what happens in that substrate changes. There are multiple zones in the substrate some of which are aerobic and others, usually between such zones, are anoxic. This arrangement makes perfect sense when one considers it fosters the complete nitrogen cycle. This is similar as to how ammonia and nitrite oxidizing bacteria in a biofilm are found in close proximity to each other.
 
One way to understand how denitrification usually occurs in a tank is this way. As the water passes through media that is bacteria laden the various bacteria in anaerobic process use up the free oxygen. As the water moves from the aerobic areas of the media through the anoxic ones, the free O has been used up and what remains is the bound O (as nitrate) that the bacteria use for denitrification.
 
Here is an old study (1999) showing how rooted plants in fw often stimulate the above http/Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L. But if you want a decent less scientific explanation of what this study showed, Dr. Hovanec offers it on his site here http/www.drtimsaquatics.com/resources/library-presentations/aquarium-hobby/aquatic-plants-nitrogen-cycle

 

[Ruskull]

Nitrates are best kept at 0, but anything under 40 ppm is "safe". 

 
Zero?  Not if you plan to keep any plants..................
 
It's completely normal to have nitrates in a planted tank, or any tank for that matter.  The idea is to not let them get too high and 40 ppm is not a lot for most freshwater fish.

 

[Ruskull]

 

My understanding is that when a plant can't get enough nutrients it releases sugars? into the water and that's what promotes algae growth. (am sure I'll be corrected if that is wrong)

I've never heard that before. Any chance of a link to where you read it?
As far as I know, the relationship between plants and algae is not very well understood and probably too complex to explain in simple terms. If there is indeed a simple explanation like plants releasing sugars then that would be cool to know! The limit of my current understanding is that algae are opportunistic, like parasites, taking advantage of plants when they are not healthy.
 

 
Healthy plants out compete the algae, or at least that's the idea.  That's how I understand it anyway & I've seen it in my tanks.

 

[daizeUK]

The odd thing is how do they out-compete?  When I hear the words out-compete I assume that there is a resource being consumed by one party with insufficient left over for the other, but in this case we know that algae needs very few nutrients, fewer than plants, and algae is successfully controlled in many tanks with a deliberate excess of all nutrients.  So it can't be a case of the plants using up all the nutrients, it must be something more complicated.
 
Allelopathy (sp?) is something I hear mentionned frequently but I'm not sure that this fully explains what is happening either.

 

[TwoTankAmin]

The denitrification process is anoxic when nitrate is involved. Anoxic means no free oxygen but plenty of bound oxygen. As I quoted above:

 
The rate of the denitrification reaction is relatively fast when there is no free oxygen present (< 0.5 mg/l is ideal).  The denitrification rate drops to zero when the dissolved oxygen level reaches 2.0 mg/l.

 
So denitrification can occur when O is there but not very much. The bacteria involved are normally aerobic. However, when O is insufficient these bacteria can use the O part of NO2. Thus they are using the nitrate. However, when the is no O and no nitrate, that bacteria switch to using sulfates and the result of this is the nasty toxic gas we do not want.
 
In sand substrates there is no O after a 1/2 inch depth or less. Sand compacts more easily than gravel. So there will be little or no O or nitrate in ones plantless substrate beyond a depth of .5 inches or less. As a resul,t in deeper sand the only possible denitrification end product is not nitrogen but hydrogen sulphide (rotten egg gas). Again it matter whether the sand has some form of aeration happening. Without this, sand deeper than .5 inch can become anaerobic and the deeper it is, the more likely is is to happen.
 
As for the plants outcompeteing the algae, this is really no know/proved. If you read what Tom barrs thinks/says you will find this:
 

 
Are they competing at all?
Are they in the same/similar ecological niches?

Why is there more than 1 type of algae?
Why is there more than one type of aquatic plant?
Why are many aquatic systems dominated by very low species diversity(both natural and man made water ways)???

The fact of the matter is that folks do not know the answer to this.
I do not, but some hobbyists like to act and suggest that they do, when in fact, they have very little humility and understanding about the matter.
And I often have torn them new ones over it.

The only researchers I'm aware of that have a chance at getting at these questions are at UF in Gainseville.
Crisman is honing in on CO2 and the variation, good guy and some of the other folks there are retiring soon.

But there's some really hard things to try and test to answer some of these questions definitely, the same is very true for allelopathy.
Our systems are much more transient and easy to replicate, nature and old undisturbed locations that have trees and sediments that are 1000 years old??
Very tough. Plant Ecology is tough business. Competition is not easy to study and measure overall.
This same question has been asked many times. Going on 15+ years and counting.

Everyone has long thought in nutrocentric terms, but this has not been the case for 15 years and in natural systems was also disproven to have any correlation(see: http/fishweb.ifas.ufl.edu/Faculty%...macrophyte.pdf )
They Concluded that plants define the system, not nutrients. I concur and oddly agreed with them, they with me when I 1st discussed this, I was blown away, I thought there's be a heated debate, but nope, they had even more support from natural systems, myself, from aquariums.

Now how the plants are able to do this is not clear.
That has not been answered.

I think allocation of nutrients and Carbon from CO2 plays some role.
Algae might be able to "tell when someone else is there" in high enough density for it not to be a good time to germinate their spores and grow/bloom.

If this "someone" suddenly stops growing for a awhile, they can tell that also.
This is also true for algae-algae and perhaps plant-plant systems, not just algae vs plants.

Messing with CO2 supply funksup virtually every pathway in plant biochemistry.
Plants adapt to specific levels, and if those levels are changed often, too frequently, this leads to poor growth.

Nutrients?
To some degree also, but less so.

Most of the so called smoking guns have been tested and remain very inconclusive.
Aquarist have extremely bad control set ups, particularly the clowns and bozos who claim they know it all about algae.
I know if I focus on the plant needs, I will not get algae, but I do not know why really.

There's a difference, I do not seek the answers, I seek to understand the questions.

from http/www.barrreport.com/showthread.php/8148-What-limits-algae?s=f597615a666d94914d248519b42dc741
 
Basically it appears there are other factors, less well understood or researched which appear to be at work. But what it seems to boil down to is that by keeping plants in good condition by not limiting what they need, the algae seems not to be able to thrive. Let the plants suffer and the algae can take advantage.