Ammonia And Plants

[jonnyf84]

hi, i have just added some Cuba (HC) to my tank, it is cycled but i am waiting for the rest of my plants and pressurized CO2 before i add any fish, this means i am still dosing Ammonia to keep the filter running, will the ammonia harm the plants or will they use it as food?

many thanks,
jonny

 

[waterdrop]

The 5ppm or less level of ammonia added during fishless cycling shouldn't come anywhere near harming plants I don't think. Plants will use a bit of the ammonia themselves but you'd have to have a very heavily planted tank before they would disrupt the process of the bacteria getting ammonia for the fishless cycle. Also it would have to be pretty heavily planted before the feedback you're getting by testing for ammonia etc. would be confused because of the plants taking up ammonia.

Plants can use both ammonia and nitrate(NO3) as an N source. Usually ammonia is much preferred by the plant as opposed to nitrate(NO3) but this also varies by plant species I believe. Some of the experts here could probably say how universal this preference is. I'm not sure about nitrite(NO2) uptake by plants (would be interesting to hear about that too!)

I'm not very experienced, but I believe one of the concerns with new tanks is that the plants will be starved of nutrients relatively more easily. Depending on the substrate (eg. if its plain gravel or sand for instance, as opposed to having nutrients added/provided) there is little buildup of debris material that plant roots can use as "backup" if the water column is insufficiently dosed with fertilizers. Sometimes when setting up a tank, aquarists have not yet figured out their CO2 or their fertilizer plans and so the new and cycling tank is "too clean" an environment for the plants I think.

~~waterdrop~~

 

[aaronnorth]

but you'd have to have a very heavily planted tank before they would disrupt the process of the bacteria getting ammonia for the fishless cycle.

If you get to that point then you can add a low biomass of fish anyway (without adding ammonia) because the plants will use it so it will be safe for fish, sometimes called a silent cycle.

Plants can use both ammonia and nitrate(NO3) as an N source. Usually ammonia is much preferred by the plant as opposed to nitrate(NO3) but this also varies by plant species I believe. Some of the experts here could probably say how universal this preference is. I'm not sure about nitrite(NO2) uptake by plants (would be interesting to hear about that too!)

Preffered Nitrogen source in order is NH3, NO2 then NO3 - so yes nitrite is used. They prefer ammonia because they do not have to use as much energy on converting the nutrient into nitrogen alone.

 

[waterdrop]

Oh, so they DO like to use nitrite(NO2) and in fact prefer it over nitrate(NO3)? That's interesting!

But its true, isn't it, that different species of plants have differing preferences for these isn't it? I think I've heard that some plants will take up some nitrate much more readily than other plants.

And overall, even if a tank is really heavily planted and healthy, it still usually falls a little short of being able to go without a biofilter, right? I mean, I know there's obviously another major variable here in the fish load, but what are some examples? How does one think about this?

For instance, it seems clear to me that the folks that like to try to go the natural route, as opposed to high tech, will often say that a small, slow internal filter will bridge the gap between what the plants can take care of and what will keep ammonia and nitrite at zero for the fish, but is that an accurate representation of the gap? Does it get closer and closer (ie. less and less filtration would be needed) as the volume of the planted tank gets larger and larger (well, I guess obviously, if the fish stock size remained same...)

 

[Dave Spencer]

Oh, so they DO like to use nitrite(NO2) and in fact prefer it over nitrate(NO3)? That's interesting!

Plants do not essentially take up any NO2, certainly not in preference to NO3. No2 is, generally speaking, a toxin. NO2 uptake has been tried on many species of plants, with no real signs of NO2 uptake.

Tests have shown a preference for NH4+ as a source of N at levels between 0.5ppm and 5ppm, which are relevant figures for somebody adding ammonia for a fishless cycle. Below 0.5ppm, which is where well maintained tanks run, the preference is for NO3, with the residual NH4+ being taken up by the filter bacteria.

As you suggest WD, there will be differences between plants in terms of when NH4+ is preferable to NO3, and vice versa. I am only aware of testing being carried out on Elodea nuttalli.

And overall, even if a tank is really heavily planted and healthy, it still usually falls a little short of being able to go without a biofilter, right?

Biofiltration is still important, as indicated above.

Dave.

 

[loraxchick]

I have a 6 gal set up heavily planted with Elodea, water wisteria and some other fast growers, DIY CO2 and ferts. it houses a male betta and three cories. had ZERO levels for five months+ with no biofiltraton. that is until i had a terrible ice storm which knocked our power for 80+ hours, the result, HORRIBLE BGA outbreak. so now have a sponge filter and going to do a blackout in a few days. When my plants wree all healthy, i had no need for biofiltration. But i wont try it again. this algae stuff's a pain!

 

[aaronnorth]

But its true, isn't it, that different species of plants have differing preferences for these isn't it? I think I've heard that some plants will take up some nitrate much more readily than other plants

plants such as ambulia are considered as "nitrate busting" plants so yes plants do have different preferences.

 

[waterdrop]

Plants do not essentially take up any NO2, certainly not in preference to NO3. No2 is, generally speaking, a toxin. NO2 uptake has been tried on many species of plants, with no real signs of NO2 uptake.

OK, good, this agrees with some book reading I was doing.

 

[plantbrain]

I have seen many folks do FC with NH3 and then they have full planted tanks, later they get Green water, particularly if they have high light, PC' lights etc.
They measure the "cycle", add more NH3, then they get this nice NO2 spike starting at about 1 week or so.

If plants are using it, why does it build up?
It only goes away when the bacteria that do NO2=> NO3 transformation become established. Then you start seeing NO3..........
This is a simple common sense test and observation you can do to see if the plants use NO2.

FC is a waste of time and often leads to algae issues for many.
Do not do it for planted tanks, the plants have plenty of bacteria on their roots and leaves already, these will settle in and the plants will directly remove and keep all the NH4 below detection limits.
And if you do do it, do it in a small bucket for the filter only, no need to pollute the entire tank.
The bacteria population will drop way down and equilibrate with the load from the fish, the plants will dominate the NH4 removal though.
The filter is mostly a back up and a good way to process NH4 at night/other waste products.

Regards,
Tom Barr

 

[aaronnorth]

Duckweed (lemna minor) has been grown in media containing NO2 & NO3, and it took up NO2 in preference over the Nitrate. When it was grown with just ammonium & Nitrite, it took up both nutrients about the same rate, now i know this cant be generalised for all plants, but it does show that NO2 is taken in by plants. It also means that less of the plants energy is needed to convert the Nitrite back ino ammonium (a plant must convert both nitrites and nitrates to ammonium before it can use them to make its proteins.)

So this comes back down to the plants personal preference...