# Nitrates in water from fish - do I need to add more?



## Surya (24 Aug 2018)

I have a 240 litre tank and a full stock of fish, and my nitrates at the end of the week are 20ppm. I do a 50% water change every week. So they basically never fall below 10ppm. Ammonia and nitrites have always been 0 since cycling. 

Does this mean that I don't need to add a fertiliser containing nitrates? Or am I missing something here? 

I've read a lot of posts encouraging people to use a fertiliser with NPK but is that for people whose plants use up all the nitrates so there are basically zero in the water? 

(I currently use either Profito or Flourish and add extra potassium).


----------



## oscarlloydjohn (24 Aug 2018)

It depends, do your plants look like they need more nitrates? There is no harm in adding more as a contingency, I have had my tank up to 80ppm nitrate with no problem (nitrate from fertiliser not fish waste, fish waste would definitely be a problem). If you are running CO2, it may be worth adding some N and P to make sure they don't run out. Otherwise, there isn't much need if your plants are satisfied as they are.


----------



## Surya (24 Aug 2018)

oscarlloydjohn said:


> It depends, do your plants look like they need more nitrates? There is no harm in adding more as a contingency, I have had my tank up to 80ppm nitrate with no problem (nitrate from fertiliser not fish waste, fish waste would definitely be a problem). If you are running CO2, it may be worth adding some N and P to make sure they don't run out. Otherwise, there isn't much need if your plants are satisfied as they are.



Thanks - is there a difference between nitrates from fish waste and nitrates from fertiliser? Is it not the same chemical compound? I'm not running pressurised CO2 and my plants look OK, just slow growing which I guess is normal for low tech.


----------



## oscarlloydjohn (24 Aug 2018)

Surya said:


> Thanks - is there a difference between nitrates from fish waste and nitrates from fertiliser? Is it not the same chemical compound? I'm not running pressurised CO2 and my plants look OK, just slow growing which I guess is normal for low tech.



There definitely is a difference, but I'm not sure exactly what the difference is. I suppose it is organic vs inorganic nitrogen. I have read of Tom Barr running his tank at 160ppm nitrates without any problems, and I have based my ideas on this and my own experiences.


----------



## tiger15 (24 Aug 2018)

All nitrate is chemically the same NO3 regardless of the origin, but the journey to get there is different.  If the origin is fish waste, it has to pass through intermeidiate stages of organic nitrogens, ammonia, and nitrite, and each can trigger algae.  So adding inorganic nitrate do no harm as it bypasses all bad intermediate stages.  If dosing nitrate as KNO3, it also adds K plants need that is likely deficient in fish waste.  I said “likely” because there is no affordable test kit for K to verify.


----------



## dw1305 (24 Aug 2018)

Hi all,





oscarlloydjohn said:


> There definitely is a difference, but I'm not sure exactly what the difference is. I suppose it is organic vs inorganic nitrogen.





Surya said:


> Is it not the same chemical compound?


There isn't any difference when the plants take them up, they can only take in nutrients as ions and every NO3- ion is the same as every other one, the ions don't "know" which compound they came from.

You will always have some ammonia production from the fish, if you have healthy biological filtration (plant/microbe filtration is more efficient than "microbe only" filtration) the plants will take up both NH3, before it enters microbial filtration, and NO2- and NO3- resulting from microbial nitrification. There may be advantages in plant growth to having an ammonia source (often urea, have a look at <"Spezial N - Nitrogen Fertilizer">), but this is balanced by potential toxicity issues to livestock.





oscarlloydjohn said:


> It depends, do your plants look like they need more nitrates?


That is really it.You can use a floating plant as your indicator of nutrient level, it isn't CO2 limited, it does away with needing to test and it gives a sensitive indication of nutrient levels. I use it as a technique for when to feed the plants, I called it the <"Duckweed Index">, but it really is a simple as *green leaves = healthy plant*. There is further discussion of this in <"High Nitrate?">, but the LCC chart below summarizes it.

"_This is the Leaf Color Chart (LCC) is used to determine the N fertilizer needs of rice crops. LCC has six green strips, with color ranging from yellow green to dark green. It determines the greenness of the rice leaf, which indicates its N content_." from: <"http://dkagri.blogspot.com/2015/02/nitrogen-n-fertilizer-is-important-in.html?view=timeslide">.




 

cheers Darrel


----------



## Surya (25 Aug 2018)

Thanks everyone, that's really helpful.


----------



## tiger15 (25 Aug 2018)

I like the duckweed indicator idea, and it's interesting that rice farmers are using it too.  I can use Amazon frogbit as indicator in my low tech shrimp bowl, but no floater is available in my high tech tank.  Is there other indicator plants besides floaters?

I posted the same OP question before and  experienced plant keepers told me to disregard fish waste and dose N and P regardless.  The rationale I was told is that dosing inorganic N will do no harm.  I agree but it can be a waste.  Now that I have heavy fish stock and my pre water change N is as high as 40 - 80 ppm, so I will experiment halving N dosing to see how the plants do.  Not dosing N at all is not good because I do 75% WC weekly and I am afraid that too drastic N drop can confuse the plants physiology.


----------



## Matt @ ScapeEasy (26 Aug 2018)

High levels of N cam be harmful to nitrate sensitive fish species. Most cichlids in my experience do not appreciate high N. Remember whilst this is the outcome of the nitrogen cycle that does not mean it is totally harmless, just far less harmless than ammonia ie. you can have it in higher concentrations in the tank before it causes harm.


----------



## dw1305 (26 Aug 2018)

Hi all, 





tiger15 said:


> I can use Amazon frogbit as indicator in my low tech shrimp bowl, but no floater is available in my high tech tank. Is there other indicator plants besides floaters?


If you have an open top tank you can use an emergent plant, it just needs to have access to atmospheric CO2. Diana Walstad wrote about it as the <"aerial advantage">.

In a high tech tank you shouldn't really have any deficiencies, so the Duckweed Index becomes less useful than it is low tech. 





Matt @ ScapeEasy said:


> High levels of N cam be harmful to nitrate sensitive fish species. Most cichlids in my experience do not appreciate high N. Remember whilst this is the outcome of the nitrogen cycle that does not mean it is totally harmless, just far less harmless than ammonia ie. you can have it in higher concentrations in the tank before it causes harm.


 I like low nutrient (including NO3) levels, the main problem is in trying to tease out the actual toxicity of nitrate (NO3-) it is only really aquascapers that add NO3 containing compounds to their tanks. 

In the tank high levels of nitrate are usually the residue, the <"smoking gun">, from a previous ammonia spike.  In fresh water rivers etc. high levels of nitrate usually occur with high levels of other pollutants. 

cheers Darrel


----------



## tiger15 (26 Aug 2018)

Matt @ ScapeEasy said:


> High levels of N cam be harmful to nitrate sensitive fish species. Most cichlids in my experience do not appreciate high N. Remember whilst this is the outcome of the nitrogen cycle that does not mean it is totally harmless, just far less harmless than ammonia ie. you can have it in higher concentrations in the tank before it causes harm.



What you said is generally right.  Nitrate is mildly toxic to fish, but not just cichlid and many other non cichlid are just as sensitive.  So any sustained high nitrate is bad for fish, not that the fish will get sick immediately, but their immunity is compromised making them susceptable to infections.

But there is a big difference between nitrate from fertilizer and from fish waste, not that NO3 is any different, but the journey to get there is different.  High nitrate from fish waste is an indicator of overall pollution.  If nitrate from fish waste is high, it’s an indicator of the accumulation of other unknown and untested pollutions such as heavy metals, tds, organics, COD, BOD, bacterial count, or harmful pheromones.  I have been cichlid keepers for decades before expanding to plants, and learned that if I don’t do frequent WC to reduce nitrate, my fish will get sick and fry won’t grow as fast due to pheromones suppression as hypothesized. 

But as Barr has pointed out, sustained high nitrate from inorganic fertilizer do no harm to fish.


----------

