# Questions about "mulm management"



## ObiQuiet (Oct 9, 2009)

Since my NPT is now about 1 year old, it's got a pretty good accumulation of mulm. I've vaccuumed it to keep it moderate, but realized that I have a few questions.

What I think I know:
1. Decomposition of mulm in an El Natural tank replenishes the nutrients in the soil substrate
2. It's important to have a layer of mulm over the gravel, to seep down through to the soil
3. Snails and shrimp help the decomposition process
4. Many people with El Natural tanks have deep layers of mulm (inches, even!)
5. El Natural principles don't require/recommend a clean substrate

I've read the thread here called "how clean is your substrate".

What I don't know:
a. After the gravel is saturated with mulm, is it still important to keep a thick layer above the gravel, or would it be OK to have just a little? (That way I could see the nice gravel I chose so carefully  )

b. Does it help or hinder decomposition to stir the stuff around manually? (I do this to even out places where it accumulates)

Thank you,
-ObiQuiet


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## ObiQuiet (Oct 9, 2009)

I found this 2004 thread that has some good perspective on my questions:
http://www.aquaticplantcentral.com/...ns/1621-mulm-valuable-compost-food-algae.html


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## mudboots (Jun 24, 2009)

I've got tanks with no water movement and still don't have that much mulm, so maybe you have too much bioload inputs. Not that it's a bad thing in an El Natural, but certainly it can't hurt to remove some of it to see your gravel.


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## ObiQuiet (Oct 9, 2009)

mudboots said:


> certainly it can't hurt to remove some of it to see your gravel.


Thank you... when I read what you said, I'm no longer sure why I was so worried about it...


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## brenmuk (Oct 7, 2008)

I have some mulm in areas of my tank where the flow is poor but most of the gravel is visible and I don't have any major algae problems.

However earlier this year when I had problems with my filter blocking up (thanks to some plecos digging up up the soil layer) I noticed a build up of mulm and a slow down of plant growth coupled with the snails and the fish hanging around the surface.

I concluded from this that the lack of flow/filtration meant a build up of mulm which in turn caused low oxygen levels which stressed the fish. 
I bought a bigger filter and saw big improvements in plant growth, the fish immediately perked up and the snails went back to roaming around the gravel.

So I think a bit of mulm is fine in an el natural tank but excessive amounts can be a sign of inadequate filtration/low O2 levels. 

Ideally you want the mulm broken down fairly quickly to release nutrients/CO2 for the plants. Removing the mulm removes a source of nutrients for plants so having mulm build up or having to vacuum it is not ideal.


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## aquabillpers (Apr 13, 2006)

I remove mulm that accumulates in depressions and near plants and rocks. I don't believe that it does any harm, but I find it unsightly.

For the nutrients in mulm to be of much value to plants, they have to be accessible to the roots. The top layer of the substrate can absorb only so much, and the excess on top of the gravel doesn't help anything.

BTW, I never stir my gravel. I uses 2mm - 2mm "buliders" gravel, and the mulm easily slips between the grains and into the soil part of the substrate.

Bill


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## ObiQuiet (Oct 9, 2009)

Thank you for the replies. 

What you say about having an excess on top of the gravel make sense -- don't need that. 

I guess it's not reasonable to have an El Natural with no filtration/circulation AND also avoid the mulm accumulation. That would require an extremely light bioload, I see -- or something like the balance that mudboots mentions. 

I'll start by vacuuming, and then I'll stir the water up and start the filter for a few days.

I'll also take note of what the snails do -- I wasn't aware of the O2 reduction due to the decomposition.


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## lake_tuna (Mar 18, 2010)

So, how do you get this mulm accumulated in the first place? I've been feeding my fish a lot, but they eat most of the flake food I give them. I'm afraid they're might blow up from full stomach if I give them more because on some (ones that are not shy) of them after feeding, they look like they're going to burst.


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## ObiQuiet (Oct 9, 2009)

Well, in my case the keys seem to be:
* 80% stocking level (aqadvisor.com)
* No circulation
* No filtering
* Rarely vacuuming
...for 8 months.

Since food never hits the bottom, everything has either passed through a fish or through a decaying plant to get down there.


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## aquabillpers (Apr 13, 2006)

To paraphrase a very learned person, "Mulm happens." 

Just keep feeding the fish a proper diet and don't worry about it.

Bill


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## JERP (Feb 4, 2003)

In lieu of a larger filter, I put a small ~$25 reef pump on my light timer. My mulm and algae issues went away.


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## ObiQuiet (Oct 9, 2009)

JERP said:


> My mulm and algae issues went away.


Wow, just from the extra circulation? How long before you saw improvement?

-ObiQuiet


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