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My understanding is ammonia is a preferred food of plants - so this begs the question just how fast do plants consume ammonia and is the rate fast enough and sufficient to negate the need for a biological filter ?
Smaller Walstads use this concept. Many vases are super successful with 0 filtration, 0 ferts, 0 CO2 and only (at the most) supplemental lighting. Larger tanks benefit from powerheads to aid in oxygen exchange but don't require filtration either. My old days (stopping about a decade ago) were filled with very successful unfiltered but heated Walstads.
 

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Any well-planted tank can eliminate the need for biomedia in a filter and, yes, plants do prefer ammonia/ammonium as their primary nitrogen source. Plants will take-up NH3/NH4 at a faster rate than BB. However, because the flow is so strong in a filter, more BB develop there, which will strip out much of the NH3/NH4 before plants can use it, leaving the plants more dependent upon nitrate. Additionally, in all tanks, BB develop everywhere, e.g; tank surfaces and in the substrate. If biomedia are not used, there will be more BB in these in-tank areas.

I have run my tank, for many years, without biomedia in my canister filter. My filters' only purpose is to serve as a pump and as a mechanical filter for detritus, and even the bulk of this is captured by the stainless strainer at the filter intake (for easy cleaning).
 

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A few terms need defining. When you say 'biological filtration' do you mean things that are specifically marketed as biological filtration such as ceramic tubes, etc, or do you mean anything stuffed inside a filter?

If you mean the ceramic bits people stuff inside filters then it's an easy answer. You do not need that, but not necessarily because of plants. Bacterial will grow on anything, there is no magic to the stuff marketed as biological media, it's just more surface area and we frankly have no clue just how much surface area we really need in a tank to filter it appropriately based on any conceivable bioload. But what we do know is with planted and aquascaped tanks, we almost always (I hesitate to say always just because maybe there is a situation when it hasn't happened) exceed the minimums.

That said, any tank that is at least 10 gallons will benefit from some amount of water movement, most tanks smaller then that can get away without water movement but its still a little helpful. Most common form of water movement is a filter.

Personally I find ceramic media useful for seeding new tanks but don't bother to keep it in filters for any other reason. I prefer sponge which does a fine job of growing bacteria and is easily cleaned while also providing mechanical filtering.

Anyway while plants will eat ammonia they will at the same time eat nitrites and nitrates. Its not like they drop everything else and only eat ammonia when it is present. So relying on them as the soul source of ammonia removal (as opposed to a cycled tank) is not advisable.
 
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