so, what exactly is mulm

[Magnum Man]

it seems some fish / maybe some tanks create more of it... is it actually fish waste being broken down by bacteria ( my guess ) plus with some organic plant material added??? not sure if some fish produce more of it by species, or if it's only produced by size, and thus the volume of waste??? raising Tilapia, and over feeding them for grow out, produces a lot of mulm... especially noticed when the fish are smaller, and in traditional aquariums, with traditional filters... in my larger grow out tanks, mid season, I change out about 2 square feet of floss per week, that get blinded over... I've noticed a large amount being produced in my barb tank, which is at a normal aquarium feeding schedule, and not heavily stocked yet... the Tin Foils are large, but not near as densely populated as the Tilapia tanks can get... makes me question if Carp like fish produce more, or the type of waste that causes mulm... I know from butchering Tilapia, that they are an oily fish... wondering if those oily fish produce more mulm...

also some fish eat the mulm like it's candy, which I've found out by just changing the cartridge rather than pulling the whole filter with hang on back filters... no one has died eating it, so it must have some nutritional value???

 

[Magnum Man]

this is an interesting article... although it falls short of answering all my questions... all my tanks are pretty much high flow tanks, so the only accumulation is inside the filters, or on the floss prefilters in the Tilapia set up...

Mulm in Dirty Fish Tanks: What Is It and Should You Get Rid of It

Mulm is a dirt-like substance that comes from decomposing organics in an aquarium. Find out whether it’s harmful or helpful & how to hide its appearance.

www.aquariumcoop.com

 

[Back in the fold]

Mulm just is . It’s stuff from anything and everything . Some guys say don’t worry about it and a little is okay but being as my aquariums are small I siphon it all out .

 

[TwoTankAmin]

For mulm to become fertilizer it needs to go into the substrate not just on the surface. Here is the over simplified explanation. Think about ammonia in tanks, from where does it come? The answer is most from the breakdown of organic waste. And what do we know about this process? We know it produces ammonia. And how is this handled in a tank? It is used by bacteria and, if we have them, plants and algae use it.

So, mulm is essentially plant food. As I said this is an over simplification. ANother way I might put it is that mulm is nature's fertilizer. The problem is that is takes some time for the mulm to be accumulated when we start with clean substrate.

If one has no substrate than what mulm can be called is dirt. In a bare bottom tanks it has no role to play and needs to be removed.

edited to fix typos

 

[Innesfan]

Yes, mulm is the general organic detritus of a seasoned aquarium. It does have its benefits, espeically if you have small biofilm grazers (as I do) such as Nannostomus or if fry are present. Many of our commonly held species are detritus eaters including many characins, barbs, livebearers, cichlids etc.

 

[Naughts]

I think of mulm as the processed waste, it is no longer decomposing and does not harbour harmful bacteria. It is inert, has nutritional benefits for plants and supports infusoria and microorganisms that benefit a balanced ecosystem. In the compost heap analogy it would be the finished compost - fine, silt-like dark particles with no malodour and having been broken down in various processes for many months.