# Nitrate and gravel vac'ing hypothetical question



## hollyfish2000 (Aug 23, 2007)

I am fanatical about changing the water in my African tank frequently with gravel vacs each time. I'm also very happy to see the poop going up the tube and out of the tank! 

Now, I'm somewhat under the impression that removing the waste is important to keeping nitrates low. That just removing and replacing water is not the whole picture. So I have a question: Say you have two identical tanks, with identical stock and identical cleaning schedules. But with one you gravel vac every time and with the other you don't gravel vac at all, just remove and replace water. In this case, will the tank without the gravel vac end up with significantly more nitrates?


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## MalawiLover (Sep 12, 2006)

In short-yes.

Long answer-Nitrates come form other sources than just the poop. As the fish breathes and urinates ammonia is added to the water and eventually get turned into nitrates. Leaving the poop and just letting it break down will cause a huge amount of additional ammonia to add to the nitrate level. This will make your constant level of nitrate much higher, by only diluting the water, the nitrate level in the non-vacuumed tank will climb higher and faster before each water change. Over time the non-vacuumed tank will continue to increase in its base nitrate level, where as the vacummed tank will remain constant.

Did that make sense?


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## Toby_H (Apr 15, 2005)

In short - I completely agree with MalawiLover

Solid waste (such as poop & uneaten food) slowly breaks down releasing ammonia as it doesâ€¦ removing the solid waste before it breaks down removes this ammonia source, preventing it from being converted into nitrites and finally nitratesâ€¦

Yet, as MalawiLover described, there are other ways ammonia gets into the water from the fish. So no amount of mechanical cleaning will completely remove all of the ammonia source. Which is a good thing as our bacteria colonies need a steady food source.

Cleaning waste from filters will also remove an ammonia source before it breaks down into ammonia (or at least before it completely breaks down).

It sounds to me like youâ€™re a bright guy (or gal) that understands the mechanics of keeping a fish tank clean and healthy


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## prov356 (Sep 20, 2006)

You'd have to also assume a decent amount of oxygenated water could flow through that detritus buildup, and typically, it wouldn't . You'd more than likely end up with anaerobic pockets where denitrification would occur and the nitrates would be converted back to nitrite.

Also keep in mind that it's not just about the nitrates but also about dissolved organics. Nitrates are just the easy thing for us to measure. If someone were to try this and the two nitrate levels weren't significantly different, it would be erroneous to conclude that vacuuming the gravel didn't matter. Leaving organics in a closed environment can only result in deteriorating water quality whether nitrate tests reflect that or not.


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## hollyfish2000 (Aug 23, 2007)

Thanks. That's what I thought! I just have a lot of time to muse about things as I vac my gravel!


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## Toby_H (Apr 15, 2005)

The more you think about something.. the better youâ€™ll understand it...
The more you understand it, the better you can prevent problems...
The more problems you can prevent, the more time you have to enjoy your hobby...

I'd much rather think than work 

Thanks for the think breakâ€¦


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## remarkosmoc (Oct 19, 2005)

prov356 said:


> You'd have to also assume a decent amount of oxygenated water could flow through that detritus buildup, and typically, it wouldn't . You'd more than likely end up with anaerobic pockets where denitrification would occur and the nitrates would be converted back to nitrite.


Seems possible, except for the part about turning back to nitrite (anaerobic bacteria eat the nitrates and produce N2 nitrogen gas, which would exit the aquarium). It would actually be neat if you could intentionally produce a layer of the substrate with just enough flow to be anaerobic enough to act like a nitrate filter and keep the tanks NO3 down to zero. Food and waste in, nitrogen gas out, it would be perfect :thumb:

Ok off of my dream world, I do think that vacuuming the gravel will drastically reduce the amount of nitrates introduced into the system because that much more waste doesn't go through the bio filter process. Based on the sheer 'grossness' of the water I vacuum out if I don't vacuum for for a short a time as even a month, I think it greatly reduces the bioload. I haven't actually installed them before, but I sure like the idea of the UGJ systems to eliminate the need for actually vacuuming.

My SA/CA tank doesn't need vacuumed since my jags seem to systematically move every last piece of gravel almost weekly, keeping the nasties floating for the filters to pick up. They're my "natural" UGJ system :lol: :lol:


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## prov356 (Sep 20, 2006)

> (anaerobic bacteria eat the nitrates and produce N2 nitrogen gas, which would exit the aquarium).


There are several intermediary processes involved in denitrification, first of which is the conversion of nitrate to nitrite.

See these sites.

http://members.optushome.com.au/chelmon/Nitrification.htm

http://en.wikipedia.org/wiki/Denitrification


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## remarkosmoc (Oct 19, 2005)

Interesting, I didn't know there were that many processes, I only knew the output was N2


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## RyanR (Apr 29, 2008)

Just remember that nitrates don't come from anywhere. There are just different pathways of processing the nitrogen in fish food. Fish are just one link in the chain.

Vacuuming the gravel seems to always be a good idea. I'm amazed how much junk comes up, even after three days.

-Ryan


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## D-007 (Jan 3, 2008)

Something else to think about then:

With a very heavily planted tank, how would one go about vacuuming the substrate without uprooting the plants?

And what ever happened to the usage of Reverse Flow Undergravel Filtration?


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## Toby_H (Apr 15, 2005)

I treat plants just like other dÃ©cor that debris can settle in/underâ€¦ I clean the open areas then use my hand to swoosh water through the dÃ©cor pushing waste into the open area where I am holding the siphonâ€¦

When trying to impress someone I do back to back smaller water changes. This way I can get the big stuff out in the first shot, then when refilling the tank Iâ€™ll use the current to blast debris out into open sand. Then come through with the second water change for a final cleaningâ€¦



D-007 said:


> And what ever happened to the usage of Reverse Flow Undergravel Filtration?


I got rid of my UGF plates many moves ago well before I ever thought of reversing the flow. I would have to believe that the flow coming up through the sand would be concentrated in the low resistant (shallowest sand) areas and would be weakest around dÃ©cor where debris settles most. Iâ€™ve never tried them personally to confirm this but it seems if they worked wonderfully weâ€™d be hearing a lot more about them, but we donâ€™tâ€¦


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## D-007 (Jan 3, 2008)

Toby_H said:


> I treat plants just like other dÃ©cor that debris can settle in/underâ€¦ I clean the open areas *then use my hand to swoosh water through the dÃ©cor pushing waste into the open area where I am holding the siphonâ€¦*
> 
> When trying to impress someone I do back to back smaller water changes. This way I can get the big stuff out in the first shot, then when refilling the tank Iâ€™ll use the current to blast debris out into open sand. Then come through with the second water change for a final cleaningâ€¦
> 
> ...


I never thought of that (doh on my part :roll: )

It was years ago when I was still living in England that I used the reverse flow method, although sand was not the substrate. When I recently returned to the hobby I hardly noticed it being used anymore, so was just curious why but your answer certainly makes sense.

Much appreciated. :thumb:


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## MalawiLover (Sep 12, 2006)

The under gravel plates only work with gravels and fish that do not dig, which prety much rules out most cichlids.


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## Sammich Bite (Mar 23, 2007)

and its not just nitrates we are talking about here. vacuuming gravel has more importance than just lowering nitrates from removing the excess poop. you're also getting rid of extra stuff in there like left over uneaten food that settled to the bottom.

im willing to bet in that controlled experiment you describe not only will there be a difference in nitrates, but also a difference in algae growth as well.



> Seems possible, except for the part about turning back to nitrite (anaerobic bacteria eat the nitrates and produce N2 nitrogen gas, which would exit the aquarium). It would actually be neat if you could intentionally produce a layer of the substrate with just enough flow to be anaerobic enough to act like a nitrate filter and keep the tanks NO3 down to zero. Food and waste in, nitrogen gas out, it would be perfect


i dont think it would really work like that, because you would probably have more NO3 coming in, then nitrogen gas going out, so the nitrate would still build up over time.

however by using plants you can achieve a near-zero nitrate level almost constantly. i know of people who have heavily planted tanks where they dont change the water for a long time and the nitrates stay extremely low.


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## remarkosmoc (Oct 19, 2005)

I have plants in most of my tanks (except for my new world tanks) and the nitrates hover between 0 and 10. I still change the water regularly. I don't know what exactly what besides nitrates builds up but regular water changes keeps the fish's color looking a lot nicer.


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## BillD (May 17, 2005)

tannable75 said:


> Seems possible, except for the part about turning back to nitrite (anaerobic bacteria eat the nitrates and produce N2 nitrogen gas, which would exit the aquarium). It would actually be neat if you could intentionally produce a layer of the substrate with just enough flow to be anaerobic enough to act like a nitrate filter and keep the tanks NO3 down to zero. Food and waste in, nitrogen gas out, it would be perfect :thumb:
> 
> A plenum below the gravel bed will do just that. The key is to create an anoxious (very low oxygen) area rather than an anaerobic one.
> The depth and size of the gravel bed determines the flow rate of water through the plenum, as it tries to attain equilibrium.


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## remarkosmoc (Oct 19, 2005)

BillD said:


> A plenum below the gravel bed will do just that. The key is to create an anoxious (very low oxygen) area rather than an anaerobic one.
> The depth and size of the gravel bed determines the flow rate of water through the plenum, as it tries to attain equilibrium.


Possible yes, practical probably not, I was just daydreaming when I made that comment. I have build DIY coil denitraters in the past and they work really well. I broke mine 2 years ago when I dropped it during a move :x

Actually in the tank I don't think it would be exceedingly difficult to control the flow rate such that the it is low enough to support anaerobic bacteria, but high enough to actually do some good.


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