denitifying baqcteria

[taimoor86]

why don't denitrifying bacteria which convert nitrate back to nitrogen develop in fish tank.
i am asking this question because i have met somebody who have a well stocked tank which is 8ft long and about 1.5ft wide and high. the thing which amazed me was tht the owner of tht tank told me tht never make water change up to a year or two, just add amount of water tht has been evaporated for few days. he is using one under gravel biological filter and one cainster filter.
i am confused, any ideas about it

 

[Pufferpoison]

yeah it's called Old Tank Syndrome.

 

[taimoor86]

please explain Old Tank Syndrome.

 

[kyazh]

in a nutshell... its when you dont change water, and your nitrates go through the roof. Your fish might be okay with this, because they can get used to it, and you'll think that everything is ok. But if you try to add new fish, the will not survive. And after a while, your fish might start dying for "mysteriouse" reasons.

 

[patoloco]

Denytrifying Bacteria

Here is the carch. Nitrifying bacteria, which converts ammonia into nitrites and the nitrates is aerobic bacteria, which requires oxigen to live. Our filter are always full of oxigenated water, os they can easily thrive and feed there.

However, denitrifying bacteria is anaerobic, which mean it has to develop whenre the is NO oxigen. This is the first difficult thing to acheive. Also, their other requirements are also harder to achieve then those used for the aerobic bacteria.

But yeah, it's possible to get denitrifiying bacteria in your tank. I will read some more and will be posting back soon.

About your friend tanks, measure the water for nitrates. If those are low, maybe he has denitrifying bacteria in there. However, my best bet is the nitrates will be off the chart, almost skyhigh,

 

[Sploke]

Yes, Old Tank Syndrome...not a good thing. If you have very hard water, you can go a long time without doing water changes. The nitrates will tend to eat away at any buffer contained in the water. In my tank, I had very soft water so it didn't take long to run through the buffer. When this happened, the pH dropped far enough to kill all the bacteria in my filter. Within days, the ammonia in my tank was off the chart, my guess was someplace around 14ppm. My fish just started dropping off one day and finally I figured out why.

By doing topoffs often, and if his water is hard enough, your friend may be able to prolong this crash for a long time. However, as mentioned, any new fish added won't be able to adjust to the skyhigh nitrates, and eventually the whole thing is likely to crash, its like a time bomb.

 

[patoloco]

The nitrates will tend to eat away at any buffer contained in the water...

...its like a time bomb.

Sploke is right about the time bomb and the Ph crash. These two things will happen.

However, nitrates are not the ones that eat the buffer. It's the life cycle it self. Whenever fish breathe, CO2 is realease to the water. This reacts with water and forms Carbonic Acid. This is what will eventually soften the water and render it acidic. When the PH drop too low, the bacteria in the filter dies.

 

[Sploke]

Yeah thats what I meant

 

[Pufferpoison]

not only will your water turn acidified, when you only "top off", all the heavy metals, minerals and other TDS's keep getting more and more potent. My sister's tank was like this and i'm slowly getting her tank back up to par. If one is only going to top of for a period of time, RO/DI water is what should be used to top off, but that is not recommended. I have a RO/DI system that i use for top off's if i skip a week to do water changes (usually every week, sometimes not practical).

 

[mooman]

denitrification does occur regularly in salt tanks. At the bottom of deep sand beds, and in the interior of liverock are anaerobic areas that support denitrification. Nitrate sponges sold in LFS are little more than artificial liverock whose interior provides an anaerobic environment and eventually gets colonized by denitrifying bacteria (that's why it takes awhile to work).

Theoretically, both practices could be used in freshwater tanks. They generally aren't because:
1- freshwater fish (and saltwater for that matter) aren't terribly bothered by nitrates
2-nitrates are easy to control with WCs (which also doesn't bother freshwater fish)
3-Denitrification does nothing to eliminate DOCs (dissolved organic compounds). High levels of DOCs are what stress fish. Nitrates and DOCs are supposed to accumulate at the same rate. Therefore we use nitrates more as an indicater of overall water quality.

Aside: Deep sand beds in marine tanks are usually maitained using a screen to keep fish and inverts from digging into the anaerobis layer. This would release a tank killing amount of hydrogen sulfide (a by-product of denitrification) which otherwise diffuses slowly and harmlessly into the water. This has been known to occur in freshwater tanks where sand is too deep and left undisturbed for too long.