Substrate and ferts

[ceg4048]

Hi,
New tanks suffer from ammonia transients due to lack of a stable nitrifying bacterial population. Under high lighting this encourages algal blooms. A high biomass increases the ammonia absorption for one thing but high plant biomass also produces higher oxygen levels and higher carbohydrate (Dissolved Organic Carbon or DOC) levels which directly feeds and supports the growing bacterial populations. There is a symbiotic relationship between the nitrifying bacteria and the plants, especially through their roots where oxygen is pumped from the stem to the roots thereby oxygenating the sediment. The bulk of the nitrification occurs via the sediment bacterial colonies, so a high plant biomass encourages the bacteria. Many people focus on getting their filter media "cycled" but it's actually much more important to get the sediment bacteria cycled which takes months to accomplish properly. In fact, the sediment bacteria, like all other living things required Carbon, Nitrogen and Phosphorous and these are supplied by organic products released by the plants in the form of leached proteins, enzymes, sugars and so forth. Without the high biomass of plants and bacteria to consume these organic and inorganic products of the system the water chemistry is in a much higher state of flux. The entire tank cycling process itself is a classic example of instability as we see the production and oxidation of these nitrogen species.

Cheers,

 

[keymaker]

...it's actually much more important to get the sediment bacteria cycled which takes months to accomplish properly. In fact, the sediment bacteria, like all other living things required Carbon, Nitrogen and Phosphorous and these are supplied by organic products released by the plants in the form of leached proteins, enzymes, sugars and so forth.

Clive, thanks for your answer. The nutrients you listed that are required by the bacteria are in fact the same ones we dose every day to our tanks. Should't those be enough to provide for them - assuming they can use the organic products released by the fish instead of plants? My theoretical (!) goal is to try to find a solution with minimizing the plants contribution to the equation. I know it can't be done, but I wonder why.

The other issue is disturbing the substrate with large uprooting of all FG plants for example. How much would that affect the already established bacteria? Let's say I'm replanting all my HC covering 80% of the substrate and do a 90% water change afterwards. Would that set back the "sediment bacteria cycling" process much thus increasing algae threat?

 

[ceg4048]

Clive, thanks for your answer. The nutrients you listed that are required by the bacteria are in fact the same ones we dose every day to our tanks.

It's even more profound than that. These are the same components all carbon based organisms on the planet use, including ourselves.

Should't those be enough to provide for them - assuming they can use the organic products released by the fish instead of plants? My theoretical (!) goal is to try to find a solution with minimizing the plants contribution to the equation. I know it can't be done, but I wonder why.

Well it depends on the organism and whether they can assimilate organic versus inorganic versions of a particular element. For example plants can only assimilate carbon in the form of (inorganic) CO2. Any other form must first be converted to CO2 by enzymatic action. Animals on the other hand are incapable of assimilating any form of inorganic carbon. That's why eating a potato is good but eating a charcoal briquette isn't. We convert organic carbon to the inorganic form by exhalation of CO2 which is a byproduct of cell respiration. Actually plants cells do this as well but it's more noticeable at night when there is no CO2 uptake. Some of our friendly bacteria can uptake inorganic P in the form of PO4. The organic forms are the most appetizing though. For example if a leaf rots , not only is inorganic NH4 produced but the DNA or Chlorophyll structure disintegrates. DNA and chlorophyll are high in N. whatever remaining ATP or ADP was remaining is also immediately attacked and absorbed since it is high in P. There is constant cannibalism and predation going on in the tank at this level and it's at this level where all the work is done. Plants can also use organic forms of nutrients obviously, but it comes at a cost because the organic unit has to be broken down enzymatically. This happens more slowly and has a lower net energy contribution (because the plant has to manufacture armies of enzymes and power these reactions using ATP which also must be produced, so the yield is lower). This works OK in a low light tank because the growth rate demand is so slow. In high light injected tanks all processes become accelerated by 5X or more, so our inorganic nutrients - KNO3, KH2PO4, which require much less complicated conversions, act much quicker since they require fewer enzymes and therefore have a higher net yield.

In a way, it's folly to attempt to remove the plants' contribution from the equation. Try not to think of it that way. Instead, think about the symbiotic relationship between plant and bacteria so they are a team. The plant feeds the bacteria and the bacteria detoxify the environment. Having said that though, it is necessary to remove the excess organic products which actually have an inhibitory effect on plant growth. In natural systems the levels of these products are kept low by getting washed away or are diluted by the sheer volume of water, but in a measly 20G tank the plants and animals produce more than the bacteria can efficiently reduce. That's why both flora and fauna appreciate water changes. The more volume change the better. So many are paranoid about nutrient buildup but the real culprit is organic waste buildup. This is what triggers stress, toxic and pathogenic effects.

The other issue is disturbing the substrate with large uprooting of all FG plants for example. How much would that affect the already established bacteria? Let's say I'm replanting all my HC covering 80% of the substrate and do a 90% water change afterwards. Would that set back the "sediment bacteria cycling" process much thus increasing algae threat?

Tthe sediment bacteria, as long as they are being oxygenated by the plants don't suffer population crash just due to being disturbed. They just carry on. The effect of sediment disturbance is more about releasing ammonia, which they have not yet had the opportunity to oxidise, escaping into the water column triggering algal blooms. Bacteria are very resilient and can't be bullied. Even if you tried to stamp them out you'd have difficulty. The new tank syndrome is simply about multiplication - can the geometric increase in bacterial population density rise fast enough to handle toxic waste production. Don't forget also that removing large volumes of water (and detritus) by default removes large volumes of ammonia and algal spores as well. The bacteria are actually attached to the sediment particles, not just swimming in the water column. The vast majority of the sediment population are unperturbed by all this activity. The water column population are affected obviously and that's what often triggers cloudiness after water changes as the bacterial populations in the column re-bloom. But this is no big deal. The bulk of the work is done by the sediment and filter media population. As the plants become healthier they do a better job of oxygenating the sediment, water column and filter colonies so that the cloudiness issues ultimately goes away after a few weeks to a few months. Higher CO2, flow and dosing generates better health which then accelerates clearer water.

Cheers,

 

[keymaker]

Cheers Clive, and thank you so much! Your answer clarified many things I was wondering about for some time now.