Fishless Cycling With Plants

[faildeadly]

If I understand what I've read correctly, if I fishlesss cycle with plants, won't the plants absorb the ammonia therefore stopping the bacteria from producing? I'm looking at covering about 30 - 40% of the tank with plants.

 

[TwoTankAmin]

The bacteria will basically size to the bio load over time. If plants consume some of the ammonia, there is less for bacteria and there will be fewer of them. However, if the plants are eating some of the ammonia before the bacteria can, that means it is not in the water and not a danger to fish. So you need less bacteria This is another way of saying that plants act as bio-filters.

 

[faildeadly]

So if I try fishless cycling but notice the ammonia keeps dropping to 0 without any nitrites, it would mean the plants are absorbing all the ammonia first?

 

[JohnDyer]

Even with a lot of plants, they won't consume 5ppm of ammonia in a single day. There would be plenty left for bacteria to start growing.
However, plants need light, and with light and ammonia you'll get tons of algae.

 

[TwoTankAmin]

Not necessarily. Whatever ammonia the plants don't take up is there for bacteria. And to that extent you should see nitrite and even some nitrate (though oplants eat that too). Think of it like a sliding scale. At one end is a tank with no plants, so it needs all bacteria to handle the load. Now as you begin to add plants the slide moves away from 100% bacteria and heads towards the other end. That end of the scale is the ammonia is taken up 100% by plants. In most cases (for planted tanks) the slider is somewhere between the two ends.

Of course the wild card in this is how much ammonia one is dosing. 1-2 ppm may not result in any bacteria whereas 3-4 ppm will. As you can see it is not a hard and fixed rule. The only way to know is for you, in your specific tank, to dose and test. But if you dose ammonia and test in 12 hours and there is 0, this means the plants are taking it all and you need to dose to a higher level to have some left over to encourage bacteria.

 

[JohnDyer]

Actually, if you have enough plants to consume 5ppm of ammonia a day, do you even need filter bacteria?
From the posts on here I've seen, accidentally leaving a filter off for a day or two only results in 1 ppm ammonia at most. If your plants can consume 5ppm, shouldn't it be able to take care of ammonia by itself, without the need of additional bacteria?

 

[TwoTankAmin]

There is almost never a need nor reason to be dosing to 5ppm of ammonia. That number will result in more cycling problems than successful cycles. The thing about plants is they are not all equal in terms of how much of the nitrogen complex they will consume. Some plants, the fast growers especially, need more nutrients than the slower growers. Next comes size. Small starter plants need much less nutrients than when they get larger and well established.

Moreover, one should understand that there is a big difference in any given tank between the amount of ammonia etc. being generated vs the amount of ammonia dosed during fishless cycling. In the latter we dump a single large dose into the tank all at once. In an established tank the ammonia is produced all day long but at a much lower level. And then there is the difference in day and night cycles in a tank as well.

As to why one would want bacteria in a planted tank that can normally handle the ammonia, there are a couple of reasons. First, consider what happens to the ability of the plants to consume all the ammonia a tank is producing. For example if you remove a bunch of the plants or if you do a major pruning. Suddenly there will be more ammonia than the plants can handle. And the next step from there will be nitrite, and what will handle that? So even in most planted tanks there will be some level of nitrifying bacteria. uther, a planted tank is rarely set up with all full grown plants. As a result there will be a need for bacteria at the outset. Once the bacteria is established, even if the plant mass increases a decent amount, the bacteria will not just vanish. They are hardy little beggars and they can and do survive when food is cut off. So some will normally be around to take up the slack and if the slack increases some so will the bacteria. It is also important to realize that when we discus bacteria in a tank we are talking about a huge number of individual bacterium, we are talking about large colonies.

The other thing to realize is a tank is a finite space, the more plants and decor one adds, the less room there is going to be for the fish etc., so the less ammonia they will be producing.

It would be nice if there were exacting formulas for all this stuff. If you could know exactly how much ammonia your tank was making and exactly how much a given plant mass would uptake. But there isn't, so we have to do the next best thing- we observe what is going on, how the plants look and how the fish etc. are behaving and we have test kits. We use all this information combined with an understanding of the processes involved to determine what is going on in a tank regarding cycling/plant issues.