Plants absorption of ammonia/nitrate.

[esoxlucius]

When I last had my little hex tank set up, once it was settled down my three main parameter readings were 0,0 and 0, always. Ammonia and nitrite are obviously expected to be 0 at all times, but so was my nitrate. Why? Simply because I had a good dollop of surface salvinia, along with some algae in this tank and it mopped up my nitrates nicely.

I took that tank down some months ago, but on 1st April I set it back up. I did a fishless cycle and didn't use any existing media at all. All I added was a small amount of fish food, maybe every other day to kick start the cycle.

It worked very well. Ammonia showed up to 2ppm, then nitrite started, up to about 2ppm. As they both subsided you would usually then get a slow rise in nitrate, but obviously I didn't, because my salvinia made sure of that.

Currently, as of today, my three readings are, as expected, 0,0 and 0, see below. Basically my tank is cycled on day 27 from when I started it!

Now my conundrum....

I read that plants much prefer ammonia to nitrate. Apparently it's easier for them to absorb? So.....why did I ever have an ammonia show in the first place? Surely the Salvinia would have absorbed the ammonia as soon as my decaying fish food started releasing it?

Instead, my salvinia didn't touch the ammonia, or subsequent nitrite, but mopped up the end nitrate in quick order.

This leads me to believe that maybe not all plants do prefer ammonia after all, but are extremely effective at processing nitrate instead.

Can you shed some light on this please neutrino , duanes .

 

[duanes]

While I have no technical insight as to the what species breaks down what nutrient better than others.
I do know Salvinia has been used successfully in waste water treatment retention ponds to consume all kinds of nutrients (even liquid metals).
So......
It doesn't surprise me that you are not getting non-detectable nitrate when adding enough plants (especially the Salvinia).
Since starting my current 180 gal tank about 4 years ago, I have never detected any ammonia, nitrite or nitrate, and done plenty of API tests throughout that time.
Having used heavily planted sumps for at least 20 years, that has been my norm.
At the moment my 6 ft sumps surface is almost entirely covered in Salvinia, and water lettuce, below the surface, Vallinneria and Hydrophilia, and in between a dozen mangrove saplings, and water Lilies.
I do not dismiss the contribution of frequent, large water changes from the get go, combined with under stocking as a large factor though.

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[esoxlucius]

My limited reading up on the subject tells me that although plants, by and large, would prefer the ammonia, some are extremely inefficient and slow at processing it. I don't know if Salvinia fits into this category, my findings suggests it does!

Although water changes will obviously still be done, it is good to know that the 0ppm nitrate, thanks to the Salvinia, will mean that this tank will be devoid of any potential nitrate associated problems, if any, that it may cause further down the line.

 

[LukeOscar]

There's a fish keeper on youtube called DWSDARIUS who goes into alot of detail on this subject. don't quote me on it but i think he said aquarium plants prefer nitrite and emerged plants prefer ammonia. he also mentions stuff about plant roots being different depending on what substrate or growing media being used that can also effect what nutrients said plant prefers.

 

[esoxlucius]

I found this, quite an interesting read. It's complicated as expected, given the subject matter. It helps me understand a little better of how the relationship between plants and ammonia/nitrate works.

Plants and Biological Filtration - The Free Freshwater and Saltwater Aquarium Encyclopedia Anyone Can Edit - The Aquarium Wiki

www.theaquariumwiki.com

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[Fishman Dave]

Diana Walstad is a very well known name in planted tanks.
I have previously had fish breeding in heavily stocked planted tanks within weeks of setting up previously un cycled display tanks, with brand new filtration, having never really seen any cycling spikes - but only ever in planted tanks. (Not that this is a recommended approach).
Interestingly all my planted tanks also have much less frequent water change regimes yet much more stable and lower readings.

 

[duanes]

Above is the amount of water lettuce I remove to the compost heap @ every other day, from my planted sump.
With each handful go a lot of nitrates.

 

[aussieman57]

My "guess" would be that plants are only capable of utilizing so much ammonia. During the initial cycling process more ammonia is produced than they can absorb. Once cycling kicks in the plants are capable of absorbing some ammonia which in turn reduces nitrate production; and they also absorb the nitrate produced. The remainder of the ammonia is converted to nitrate in the cycling process.

 

[Stanzzzz7]

I could be wrong here but my thoughts on this are that root feeding plants absorb nutrients far quicker than plants that rely more on leaf absorption.
Ammonia tends to be found in the substrate and lower parts of the water column so is absorbed through root feeders in the substrate or through the leaves of plants lower in the water column.
In systems without the addition of co2 injection ,planted stem plants and rosette plants will grow a lot more slowly than floating plants on the surface.
The same I would expect of the likes of pothos and other house plants poked into the top of an aquarium.
These plants would grow much faster as a result of roots in constant contact with water and nutrients ( nitrate included) and constant access to co2 . This is why plants like Salvinia, frogbit and duckweed grow so fast and are so efficient at removing nitrate.

 

[esoxlucius]

At the end of my post #5 I added a bit of info which I think sums the basics up nicely.

Out of 33 common aquarium plants tested every single one barring four prefer ammonia over nitrate. And even then the other four were from environments which are typically very low in nutrient content. So it's pretty safe to say that ammonia is top of the menu.

And apparently leaf uptake of ammonia is far more efficient than root uptake. This makes sense really because if roots just absorbed ammonia in the substrate then that would leave ammonia in the water column, and the protection of the fish would be compromised. They've done split chamber experiments to prove this too between the upper plant and the root system.

But nitrate isn't ignored completely. Once all the available ammonia has gone the plants readily gobble up the nitrate. And during further experiments they re-added ammonia and the plants stopped absorbing the nitrate and reverted back to the ammonia, until it was all gone, then continued with the nitrate again.

Quite clever I thought.