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[APD] Re: ecosystem in aquariums

>>    As everyone knows, one of the roles of plants for
>>the well being of an aquarium is to absorb those 'harmful' substances from
>>the water column, namely ammonia (NH3), Nitrite (NO2) and even Nitrate
>>(though the least preferred source of Nitrogen). 

No, this actually reversed, NO2 is the least preferred, then NH4 at low levels that exist in our tanks, and then NO3 is the preferred form. 
You can test this your self and easily see that NO2 is not removed over a 2 week proid when no other N source is available.

Folks doing fishless cycling with planted tanks see the NO2 persist for long peroids.
At high levels of NH4, say 0.5ppm and higher, there is strong evidence that plants perfer NH4 and supress NO3 uptake but NOT at low levels of NH4, generally low enough not to kill your fish:-)

The rate of uptake is the assumed parameter that suggest preference.
You need a certain critical concentration in order to drive uptake rates at higher levels.

NH4 is not ever very high in our tanks, while NO3 is...........
This is why, at least for our tanks, that plants prefer NO3, not NH4(but will still remove it).

If you have the same concentrations at higher but equal levels(say 2ppm NH4 and 2 ppm NO3), then the plants will prefer the NH4 and supress NO3 uptake.

But if you have 0.1ppm of NH4 and 10ppm of NO3, NO3 will be greatly preferred.
Plants get use to conditions and to the NO3 availabilty and do not rely on the NH4 source if it's not present.
Plants are not static, they can change their methods to obtain the needed nutrients.
>This has led to discussions
>whether it possible to run a planted aquarium without filtration since the
>plants are substituting the roles of the nitrobacter and nitrosotomas
>bacteria in a biological filter.

Well, they circumvent their needs to some degree and remove NO3, neither of these bacteria do that, only anoxic(200-300mv) denitrifiers and autoptrophes(plants/algae, a few bacteria) will export NO3.  
I'd still suggest a filter as a backup, better them to use the NH4 should something be wrong with the plant's uptake/growth rate than the algae.

Bottom line, a filter does not hurt and it will help keep the system MORE stable than tanks without filters.
Observations also show this.

>> In fact, in aquariums which are heavily
planted and with a minimal stocking of fish, such colonies of bacteria are

Yes, plants will dominate the NH4 pool.

>> However, this is just an ideal view and very few aquarists suggest
not using biological filtration at all.>>

Well why should they suggest no filter?
You could say the same about any fish tank, just do water changes, use carbon, NH4 removers etc. 
Why not use a plant filter in that section? Remove the filter bio section and put an emergent plant in there.
Better yet, drive the plant growth better in the main tank since that is the focus here and then supplement with 3 inorganic ferts and CO2.

Then you can garden and aquascape nicely.

If your goal is to allow the tank to "balance", with the minmal work load(the lazy tank) then a non CO2 approach is better suited. Many enjoy the idea of fish waste=> plant food.

This works because the rate of growth is slower, less light, no CO2, decent substrate to get the plants established(you can forgo this and add the nutrients to the water column as well, then stop later as they are not needed).
>> However such a claim may be extended to the partial
water changes in an aquarium. Hobbyists encounter the problem of maintaining
water parameters at an optimum level suggested by the experts. I.e. General
hardness 2- 5 dh and KH 3 - 5>>

I do not know what optimals GH's and KH's are or are not really, I do research on aquatic weeds.
Generally, harder water is better for plants. I've had tanks from 1-18KH and GH's from 3-24.
No issues there.
Again, I'm not sure where you got this data, it's not supported in the research, the opposite is although.....

>>Tap water may contain very high GH and it is really frustrating to lower
such values using appropriate resins especially where relatively large
aquaria are concerned.>>

Not sure why you believe high GH is an issue.......there's no evidence to support that. 
At high KH's, plants can use the HCO3 as a source for DIC carbon when the CO2 is removed.
Ca/Mg/SO4 etc are plant nutrients not associated with any algae issues.  

But on a practical term, I've never seen an issue with higher GH/KH except with some growth of about 2-3 plants.
They still grew, ju7st not as well, but the rest of the 300 or so species I've grown did better, not worse in hardwaters. You can see this same trend in natural systems. 

Come to FL for the Plant Fest and you can see this for yourself.

>> So, assuming that the aquarium is decently planted
with the minimal stock of fish (just algae eaters and corys for example)
that it is also needed to fertilise with NPK; does it make sense to change
one third of the tank volume fortnightly?>>

Depends...........if folks add CO2.....generally yes, non CO2 tanks........no.........
The rate of growth is slower, the fish food and fish waste alone can supply the plants growth rates at this lower light/CO2.

At higher plant growth rates, we need to add more light, more CO2 and then more nutrients in the inorganic forms. 
If we added more fish, there would be too much NH4 produced.
This would be beyond the limits of the plant's uptake and the bacteria's to maintain low undetectable levels.......
Then you get algae due to trace amounts of NH4 present............

If we add KNO3 , we can have high levels of NO3 that do not cause any algae. You can test yourself to prove this to your self.

>> Remember that there will not be
excessive ammonia, nitrites and nitrates due to fish excretions? Can anyone
limit himself to just add the evaporated water with reverse osmosis or
distilled water and say make a partial water change occasionally?>>

I've gone 8 months, typically I'll go 3-6 months without a water change depending on the need to weed the tank.
I'll top the tank off with tap water(It has KH and GH, both of which plants will use).

Even these slow growth non CO2 tanks can be improved on and dosed here and there.
Fish food and the substrate alone can supply a relatively decent growth with SOME species, but I've found many of the more difficult plants not associatred with non CO2 tanks to do much better with higher GH's and KHs' and with some K+ supplementing.

>>  Some
people talk about 'aged' water. Do they mean water which has accumulated
substances not used by plants and not absorbed by filtration?>>

I "think" they mean that.
Who knows what they mean, most of "their advice"(whoever "they" are are) is highly vague.

>>  Regards,
   R. Vella>>

Tom Barr

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