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Plants replace bio-filter?

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1. I've read conflicting opinions (expert and otherwise) on whether plants will absorb the ammonia/nitrate/nitrite produced by fish/food/etc. such that the aquarium will no longer need any biological filter. True of False?

2. The biological filter helps produce oxygen for the fish. True or False.

(Man, I sound like my bio teacher in high-school. ... "Right minus Wrong"!)
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You need biological filtration as a safety net. You dont want amonnia or ammonium in the water because it helps algae more than plants.

Biological filters deplete oxygen more than help add it.
Thanks Shane. The plant vs filter concept has caught my attention because of its implications. Some have said that the plants will consume the chemicals (nitrate-trate/ammonia) which the bacteria feed on and hence, the bacteria will eventually starve and die off. Ergo, no biological filter -- even if a biological filter is running.

This means if for one reason or the other, the plants die off, the aquarium will have to go through a new cycle to build-up a new bacterial bloom. This could be deadly to the fishes especially in a well-stocked aquarium.

I'm still trying to find topics on this issue but if anyone else has thoughts on these, please post here.
The bacteria wont starve and die off. They get first dibs at any ammonia produced due to their location and simple "lifstyles". If there is a problem with the bio-filter or in a brand new tank, then the plants will consume the NH3, NH4 from the food and fish waste. You don't want to rely on the plants because as Shane pointed out, ammonia/m is the biggest food source to algae. That's where the new tank syndrome comes from. Even a tiny unfixed amount of it will cause an algae bloom. The bacteria in the aquarium will convert the NH3, NH4 and NO2 into NO3 so fast that the algae and plants never see it. Plus, this all happens, mostly, in the substrate where only hte bacteria can get at it.

Also, like Shane started, you need a bio-filter as a safety net.
Thanks for the inputs guys, I found this paragraph about this issue -

"The Bio-filter bacteria convert ammonia and nitrites into nitrates. Plants can use all three of those as their source for nitrogen. In fact, ammonia is the preferred nitrogen source for plants. If you add plants to a tank with an established bio-filter, the plants will actually use up some of the ammonia before the bacteria can convert it. That means that there will be less ammonia for the bacteria, so the bacteria colony will decrease in size. And since less ammonia is now being converted to nitrite, there will be less nitrite than before, so some of those bacteria will die off too.

"I recommend starting out with the plants doing the job of removing harmful ammonia. In order for this to work, you must ensure that the plants are growing and thriving before adding the fish.

"My plan for setting up a new planted tank involves setting up all the tank equipment, including CO2 and Lighting, then adding plants, and giving them several weeks to get established before adding any fish. During those several weeks, the plants will get their roots established, use up any nutrients already present in the water (and begin using substrate fertlizers provided), but the algae will starve, since you aren't adding any fish food, and there is no fish waste for those couple weeks. This lets the plants get a head-start on the algae, and ensures a beautiful algae-free tank."
Full text can be found here -

So based on your comments, and this article, it seems that plants will consume SOME ammonia, nitrite but not enough to actually work as a substitute for a biological filter.
I think that is correct.
To infer that plants decrease the efficacy of your bacterial colony is a bit hasty. The plants will die off long before there are not enough nutrients to sustain bacteria.

Even if you are running a healthy planted aquarium, by no means does this imply that you have no bacteria growing in your tank. As Dennis pointed out, the substrate is an area where nutrients aren't always reached by the plants, as are your filter media and the walls of your tank. Bacteria even grow on the plants themselves.

Certainly plants and bacteria consume some of the same food, but their habitats are typically very different. Where one can access a given substance, the other cannot.

These things tend to work themselves out. I have had massive plant die-outs due to neglect that didn't create either ammonia or nitrite spikes in the water. The bacteria (presumably) handled the problem without a hiccup.
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