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After a while, mulm begins to accumulate as a layer on your substrate. It is the remanants of fish poop and decayed/ing plant parts. This layer can become quite thick. There are two schools of thought related to what it is good for.

The first say that it must be removed ASAP as it will lead to uncontrollable NO3 and PO4. Students of this school will vacuum it out or use diatom filters and stir it into the water column. They also believe it clogs the substrate and doesn't allow for freshwater to mix with the substrate solution.

The other school considers is as valuable fertilizer for the plants much like compost. Bacteria is converting (recycling) the organic material into inorganic food for the plants. Students of this school don't touch the mulm unless it is getting unsightly and then only vacuum a small area.

What school are you in?
 

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I have a decent fish load in all my tanks. When I do my weekly water changes, I will siphon lightly over any exposed areas. If I do uprooting or replanting then I will vaccuum the gravel in that area which was uprooted. The uprooting can occur every couple of weeks or every 6-8 months depending on the plants. Following that routine, I haven't had any algae issues on any established tank.

My 29 gal has been set up for about 6 years without a major tear down. I started growing plants in it about 3 years ago when I learned about these boards on the web.
 

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Jeff asked me about this one back in Mar.

I feel too much can be bad in the substrate.
I disturb the substrate every few months in most of my tanks.

I trim and uproot rather than topping at a pruning habit.
This leaves some root material left in the gravel, but also pulls loose much of the detritus.

I vacuum off and remove all the mulm in the water column itself.
Some in the gravel or filter is good, but JUST like a clogged filter, too much in the substrate can be deterimental.

I think many have become enamored with mulm but excess amounts are not good and looks bad in a tank.
Doesn't matter what school you are in there.

But you can save it and dry it out and use it later when you set up a substrate.

A little to help start a tank's substrate is good(dried or fresh or a little of both).

I'm not sure what uncontrollable NO3/PO4 is.

2ppm of PO4?
20ppm of NO3?

Or the fraction of N and P the mulm is in, eg PON/DON etc rather than inorganic NO3 etc.

I treat it like compost to a certain degree but the rate of mulm production and the rate of growth in the tank will deterimine how much of the mulm waste are recycled in a planted tank.

That is the most important point.

Maintenance routines also make a huge difference.


Regards,
Tom Barr
 

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plantbrain said:
Jeff asked me about this one back in Mar.
Tom was explaining why removing excess mulm was a good idea. I just had to ask him, "if excess mulm was problematic, why he usually recomended adding additional mulm to new set-ups". No surprises there... some is beneficial, too much is detrimental.

In March I was considering if my substrate may have become too compacted or exhaused after seven years. I decided that it just needed more CO2 and better plant health to keep the roots oxygenated. This has proven true over time. I suppose one could conclude that more mulm causes problems when CO2 is insufficient and plant health neglected. It seems plausible.

I think removing excess mulm is a good idea when combating a BGA bloom.
___
Jeff
 
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