# Using denitrifying bacteria in a fishtank **URL:** \ **Category:** Factual Questions\ **Created:** [May 29, 2007, 6:04pm UTC](https://boards.straightdope.com/t/using-denitrifying-bacteria-in-a-fishtank/405952 "2007-05-29T18:04:59Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [May 29, 2007, 6:04pm UTC](https://boards.straightdope.com/t/using-denitrifying-bacteria-in-a-fishtank/405952/1 "2007-05-29T18:04:59Z")
I hate cleaning the fishtank. I know why its necessary. Fish excrete ammonia as a waste product. In the presence of oxygen, bacteria convert this into nitrite or nitate. The last step should be that denitrifying bacteria convert this back into nitrogen gas. Then I wouldn’t have to clean the fishtank. Why doesn’t this happen? ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [May 29, 2007, 6:21pm UTC](https://boards.straightdope.com/t/using-denitrifying-bacteria-in-a-fishtank/405952/2 "2007-05-29T18:21:12Z")
The type of bacteria which convert nitrates into nitrogen gas can only survive in oxygen-free environments, which aren’t found in most aquariums. Maintaining oxygen-free conditions while also keeping sufficient through-flow to get the nitrates to the bacteria is difficult, but can be done. Reef aquariums commonly do this with “live rock” - spongy coral-skeleton-based rocks which house pockets of anaerobic denitrifying bacteria within them. It’s also possible to do this with properly set up anaerobic sand beds or similar setups. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [May 30, 2007, 1:25am UTC](https://boards.straightdope.com/t/using-denitrifying-bacteria-in-a-fishtank/405952/3 "2007-05-30T01:25:56Z")
[QUOTE=AndrewL] The type of bacteria which convert nitrates into nitrogen gas can only survive in oxygen-free environments, which aren’t found in most aquariums. Maintaining oxygen-free conditions while also keeping sufficient through-flow to get the nitrates to the bacteria is difficult, but can be done. Reef aquariums commonly do this with “live rock” - spongy coral-skeleton-based rocks which house pockets of anaerobic denitrifying bacteria within them. It’s also possible to do this with properly set up anaerobic sand beds or similar setups. [/QUOTE] Research anaerobic sand beds, it seems that they are only available for saltwater aquariums. Why is this? Are there any similar set ups for freshwater aquariums? What about adding more plants.? Will this reduce the amount of cleaning I have to do? ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [May 30, 2007, 1:16pm UTC](https://boards.straightdope.com/t/using-denitrifying-bacteria-in-a-fishtank/405952/4 "2007-05-30T13:16:56Z")
It is true that anaerobic denitrification is usually only done in saltwater aquariums. I haven’t seen it done in freshwater. I don’t know if it simply isn’t possible in freshwater tanks, or just not the usual practice. [Here](http://www.wetwebmedia.com/FWSubWebIndex/fwnitrates.htm) are some suggestions for controlling nitrates in freshwater aquariums. I have experimented in the past with cycling water from the tank through a gravel bed with plants growing under bright lamps in it. This did seem to reduce nitrate buildup, although it was a complex arrangement and took a lot of fiddling with. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [May 30, 2007, 4:02pm UTC](https://boards.straightdope.com/t/using-denitrifying-bacteria-in-a-fishtank/405952/5 "2007-05-30T16:02:00Z")
Thnaks for the link. The use of elemental sulfur sounds interesting.