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The Effect of pH on Autotrophic Bacteria (The bacteria in our filters that process ammonia and nitrite)
*It is really important that you know how the Nitrogen cycle works before reading this article. You can read about the Nitrogen cycle
here.*
There are two different types of bacteria in our filters. One type, which utilizes ammonia for a food source, is nitrosifyers from the genus
Nitrosomonas, while the other type that utilizes nitrite for a food source are called Nitrifying bacteria, from the genus
Nitrobacter. Just as long as we know the real names and where they come from, I will be referring to the two different types of bacteria as either
Nitrosomonas for the ammonia bacteria, and
Nitrobacter for the Nitrifying bacteria. We can also refer to both of these types of bacteria as Autotrophic Bacteria as a whole.
Autotrophic Bacteria are extremely important in our tanks. They not only keep the ammonia and nitrite levels down, but they also produce nitrate, as an end result to the nitrogen cycle, which plants can utilize for an extra source of nutrients. Autotrophic Bacteria are essential to all life because they are the primary producers at the base of all food chains. Autotrophic Bacteria are everywhere; they are in the very water we drink and the water we swim in when we go to the lake. So, it is in our best interest to have ideal environments in our tanks in order to allow these bacteria to thrive and colonize. This will allow our tanks to run to their full potential! The fact is there are multiple factors that can affect how these bacteria grow. When we cycle a tank, especially if it is for the first time, most people want the tank to cycle as fast as possible so they can add fish. However, there is one factor that I am going to talk about, and that is how the pH of the water supply, you are using for your tank, can affect the colonization of these Autotrophic Bacteria.
All water has a pH level, either it is acidic, neutral or basic, there is going to be a level of which your pH is. An acidic pH is a pH level that is below 7.0, while a basic pH level is above 7.0, and yes, you guessed it, a pH of 7.0 is neutral. Most fish can adapt to a fairly wide range of pH, however; Autotrophic bacteria can do the same, but in most cases it takes a long time for the Autotrophic bacteria to adapt to a lower level of pH. Instead, depending on the pH level of your water, your Autotrophic Bacteria are going to act differently, until they have adapted to a certain pH level. Even further, it takes time for the Autotrophic bacteria to adapt to a pH level outside their normally operated pH range, in which case if your pH drops down below 6.0, you may experience some problems. Having a pH of 8.0-8.4 is optimal for the colonization of these bacteria, but not required, especially if the temperature is at or around 84 degrees F, or 29 degrees C. It is this pH range that is going to yield the greatest growth rates for the Autotrophic Bacteria. While most water has a pH in the mid 7’s, this is still really good and will still have fairly good growth rates. Between a pH of 6.6 to 7.0, the growth and consumption rates of these bacteria will gradually decrease, but will still yield very good results at the processing of ammonia and nitrtie . At a 6.5 pH level,
Nitrosomonas growth is inhibited. This means that the process of breaking down ammonia is going to be extremely slow. The bacteria at this state are just processing enough ammonia to stay alive, not grow or colonize to meat higher ammonia levels. Also, all nitrification is inhibited if the pH drops to 6.0 or less. This means that the nitrite processing will be extremely slow as well. So, with this is mind, it is extremely important to know the pH of your tank, and keep a close eye on it. If the pH drops close to 6.5, immediate action should be taken. Note: when the pH drops this low, and the Autotrophic bacteria drastically slow down the processing of ammonia or nitrite, this does not mean the the Bacteria have died off at all. In fact, this means that the Bacteria have simply gone into a "dormant" state where they process the ammonia and nitrite at extremely slow rates, and when the pH raises back up above 6.5 or so, the bacteria will then resume production on ammonia and nitrite at their previous capacity. However, like I stated before, Autotrophic bacteria can, and will adapt to lower pH levels, but it takes time to do so. Under optimal conditions, Nitrosomonas may double every 7 hours and
Nitrobacter every 13 hours. More realistically, they will double every 15-20 hours.
How softness or hardness of water can effect the pH.
The pH of water is always prone to changes or fluctuations, especially when we start to cycle a tank. When ammonia is added to the tank, the pH can take some nasty turns, which could ultimately effect the Autotrophic Bacteria. When water is hard, or has a high mineral content, the water has a higher buffering capacity. This means, since the water is harder, that the pH is not as susceptible to changes, as if the water was soft. If you have soft water, this means that the mineral content in the water is low, or has a low buffering capacity. This will usually make the pH drop, or make the pH fluctuate a lot more. As the cycle progresses, and you start to produce nitrate more and more in your tank, your pH might start to drop. As nitrate, the end product in the nitrogen cycle, is a little more acidic, meaning it may drive your pH down. Depending on how soft your water is, the nitrate that is being produced could potentially make your tank have a pH crash. A pH "crash" is when your pH drops below a safe level for the Autotrophic bacteria, usually 6.5, and your Autotrophic bacteria begin to slow down or stop in production all together. If this happens, follow the steps below to raise the pH level. A pH of 6.5 or less is not necessarily unsafe for fish however. Certain fish will thrive at lower pH levels, however; these Autotrophic bacteria will go into a dormant state if the pH drops below that point, usually it is a pH of 6.0 or less for extreme cases.
How can I have fish that thrive in a pH below 6.0, where the Autotrophic bacteria's production rates have decreased? Won't the ammonia level be high because of the lack of production?
Since plants use Ammonia as a source of nutrients, having a really heavily planted tank will prevent the ammonia level to rise above a safe limit. Also, if you start off cycling your tank with a low pH, the bacteria within the tank will adapt to the lower pH value, but to do so, it will take a lot longer than having a pH above 6.0-6.5.
What are some ways to raise the pH of my tank water if it drops too low?
A large water change may be the best option if you are cycling the tank. When you do a water change, the pH in your tap water will be higher than that in the tank. So, when the new water enters the tank, the two different pH levels will reach an equilibrium. This means that the higher pH in the tap water and the lower pH in the tank will average out to a new pH, hopefully higher than before. However, since your pH dropped low in the first place, that is a good indicator that your water may have a low buffering capability, or low KH. The following steps will shows ways to raise the KH of your water, ultimately raising the pH. With constant changes in the ammonia level during a cycle, the pH can be really susceptible to change. Until you get the tank cycled and your ammonia level zeroed out, the pH will most likely change a little. This is not to worry about that much, because after the cycle the pH should be pretty stable. Here is what to do if the pH is still unstable after the cycle. pH, more or less, has a direct relation with the hardness of your water. It is really important to purchase a GH/KH test kit to know the hardness of your water. If you have soft water, your pH is going to be more susceptible to fluctuations. This means, minor things added to the tank, as little as an ammonia spike, can change the pH of your water. It is best to raise the hardness of your water a little, which would make your pH less susceptible to fluctuations. There are a couple ways to raise the pH and hardness, and they are adding sodium bicarbonate (baking soda), sea shells, limestone rocks, chunks of marble or some little pieces of coral to the tank. You can even buy substrate, which is made ideally for Cichlids, that contains parts of sea shells. Any of these can increase the pH of water.
In conclusion:
It is best not to let the pH drop too low, which is usually around 6.5 or lower. If the pH drops that low the Autotrophic bacteria's production rates are going to decrease dramatically until the bacteria have adapted to the lower pH level. Like I said earlier, this takes time to do so, so it's best not to let the pH drop that low in the first place. In other words, if you are cycling a tank, and the pH drops that low, the cycle will most likely stall.
Hopefully now you will have a basic idea on how the pH level can affect how the Autotrophic Bacteria colonize and process ammonia and nitrite within a tank.
Sources:
NItrifying Bacteria
Ways to raise pH and Hardness
Autotrophic Nitrifying bacteria at low pH
-FHM
All text in this post are copyright fatheadminnow, 2009.
hmm after typing that out.. removing coral seems a lot easier... or at least taking some of it out... anyway thanks for the help... I did not add the tabs (they were disolving in a seperate Jug of tank water.
