Silt/mulm in sumo: bad or good?

[Hal3134]

I’ve got a build up of a very fine mulm/silt in my sump. Is it good (base for pods and bacteria) or bad ( nitrate or phosphate factory)?

ca=465, alk=8.0, mag=1500, nitrate=0.5, phosphate=0.03, sal=36ppt

 

[Hal3134]

Bump

 

[nereefpat]

From what I understand, supposedly inert. I have a bunch that has settled in my sump and overflows too. I suck it out on occasion.

 

[RobertP]

It is not a good thing but does not really hurt unless it is allowed to build up. Many people will tell you to keep your sump as clean as the tank and others let it collect whatever. On my tank redo I got a BUNCH of rock dust all over the sump and this even after I rinsed and soaked the rocks. I was running no filter socks for a while which didn't help catch the dust.
I will eventually clean all that funk out of the bottom of the sump but it can wait for the six month sump cleaning.

 

[Hal3134]

I'd say that it is built up. There are literally cups of it against one wall of my sump. The question is what is the effect on my water of this? All my measured stats are within norm.

 

[GeoSquid]

I have the same thing. Is it bad? I've let it build up quite a bit in the bottom of my surge/refugium tanks. Paul B had a write up some time ago about mulm and said it was beneficial but said it formed in the dark parts of his reef. Mine looks like fluffy dirt its directly under the lights. Not sure it's the same thing he's talking about.