Excess mulm

[Underwater]

I have excess mulm in my 75 gallon tank.  The only plants are water sprite and some duckweed.  I get mulm buildup in the roots of the water sprite and it makes the tank look dirty.  I've been trying to stir it up and vacuum it out, but it builds rather quickly. Anyone have any tips on reducing it?

[BigDaddy]

Prune your watersprite more often.

Fast growing plants are a good source of mulm.  Essentially, as the plant grows, leaf structure lower down on stem breaks down, decays and eventually turns into mulm.

Some mulm is good, as it is a natural fert.  However, too much as you mentioned, is a little unslightly.

I get lots of mulm around my E. tellenus (very fast growing carpet sword) and my rotala and hygro.

During your waterchanges.... instead of vacuuming the gravel deeply (which in a heavily planted tank isn't much of a requirement), target your mulm hot spots.

The other option is to get some undergravel jets or powerheads running some current along the substrate.  That will keep anything from really settling on the bottom, so it will stay in the water column until your mechanical filtration can pick it up.