"Mulm" in a Reef tank

Paul B · Jun 10, 2016

I think one of the most important, and least understood or mentioned things in a reef tank is "mulm". That stuff that grows in the dark portions of a tank if it is set up long enough. "Mulm" is a combination of algae, sponges, bacteria, pods, worms, detritus, poop and any thing else that can be propagated or grown in the dark. I realize most people would immediately get out the sponge, razor blade or grenade to remove it but there is a word I like to use to describe those people. That word is "wrong". Mulm is a natural product that you will find in the sea all over the world. Our tanks run on bacteria, algae and a food chain. Bacteria and a food chain are dependent on having a place to reproduce. Mulm is the perfect place. Rocks and glass are flat surfaces that are only two dimensional. Mulm makes these places three dimensional allowing much more space for bacteria and microscopic organisms to grow and do the macarana. (They love to dance) Pods, which are needed for any small fish also need to eat and their numbers are directly related to how much food they can get their hands on (or whatever pods use to eat with) The more food, the more pods, the more pods, the easier to keep smaller fish. Larger fish such as copperbands and angels also eat pods.
Many people try to keep fish such as pipefish, mandarins or other dragonettes in a sterile tank and while feeding them a couple of times a day with tiger pods or some other expensive food. Those types of fish will not live for long in such a tank and they certainly won't spawn which I consider the "only" criteria to determine the state of health for any paired fish.
Mulm (after a while, maybe a few years) should grow on the back and sides of glass as well as under rocks.
Here in this picture of my clingfish, the mulm appears green. It is really brownish and that fish is on the side of my tank. I brightened up the picture and turned it sideways because it was in the dark and the fish was hard to see.
There is a thick layer of it on the back of my tank where my mandarins and pipefish like to hunt. My long spined urchin also grazes there most of the time as there is not much algae in my tank for him to eat. He is many years old as are the mandarins and pipefish and they are dependent on this food source.
A sterile tank IMO is the biggest problem we have keeping certain fish healthy.
Sterile is good in an operating room but very bad in a tank.

I recently took this off Kauai Hawaii. The rocks are covered in Mulm. You can see a spotted moray eel in the center.

This was in the Caribbean. The mulm provides food for those fry.

This is off a mangrove Island in Key Largo Florida. Notice the growth on the roots.

I know many people will disagree with me. That is fine. But everything I propose I post pictures to back up my theories. None of my ideas come from re-hashed, inside the box rumors.

brandon429 · Jun 10, 2016

but what if that looks like an algae scrubber, only distributed around the tank and taking away from prized sps lps, what happens to the tank if we reject that growth solely due to looks and simply buy a retail feed to replace the awesome feed that those growth zones do provide

I think that's why people like to contain ats inside dark bubbly microwave dinner trays

for sure a tank could grow them in controlled areas and be ok but its coralline most are wanting

I get where you are going though. the caymans are uber clean reefs and look like that in places

Paul B · Jun 10, 2016

Brandon, thank you for responding. I don't propose that you see any of this in a reef tank as it would only grow in the dark. I also have an algae scrubber that grows algae, but green algae is not what I am referring to. The stuff I am talking about only grows in the dark recesses of an older tank. I see none of it in my tank unless I use a flashlight.
We also can not buy any type of food product that will mimic what is naturally in mulm as that stuff is alive and constantly reproducing microorganisms to feed the tank.
Here is a part of my reef. It is very old and yet you will see none of it unless you looked hard in the dark places where it is covering the side and back glass as well as under the rocks. All my paired fish are spawning and I attribute this mulm as part of the reason for that. I also think it has something to do with why my tank has survived so long without any crashing, disease or quarantining. It is part of the naturalness of the tank.

brandon429 · Jun 10, 2016

I cant see it=its feeding a tank that nice

= get that mulm and bottle it up lol

brandon429 · Jun 10, 2016

cryptic zones had some article stuff going on in 2006 I remember, Toonen did some

Paul B · Jun 10, 2016

I took that picture of that clingfish on the right glass about a foot to the right of that frogspawn on the right. I could not see that fish or take the picture without a flashlight which is how I took the picture. The back glass in my tank, which is also dark is also covered with the stuff. I can see numerous tiny worms, amphipods and tube worms all over it. It is the life which I have always strived to keep in the tank. The stuff we buy and can see is easy to keep. But the health of the tank is more determined by the number and variations of the tiny life that we don't normally see. If I lift a rock in my tank, I will see numerous amphipods scurrying about. Just like in the sea. I don't remember how old my long spined urchin is but he gets a good part of his diet from the mulm. So do my 3 pipefish. It's like a healthy unlimited salad bar.

Paul B · Jun 10, 2016

Of course we don't want to see that stuff growing on the lighted parts of our tank.

WetWhistle · Jun 10, 2016

Mulm will also grow in the deep sand beds as well it is just not as prolific as the dark regions. It is super nutrient dense and is a great food source for not just the food web but the corals and fish as well but an important food source for fish fry and pods. I agree it would add stability to your system for sure.

brandon429 · Jun 10, 2016

hey yours zos look good there those are short and squat as they should be looking sharp

Paul B · Jun 10, 2016

Thank you, I like my Zos to be sharp.

chefjpaul · Jun 10, 2016

Tank looks great Paul.

Nice write up as always.

Paul B · Jun 11, 2016

Hello Chef. How have you been?

chefjpaul · Jun 11, 2016

Paul B said:
Hello Chef. How have you been?

Good, crazy busy. Bought new home in Bronxville. Remodeling etc..

Are you going to pop into RAP next weekend?

How are you and the supermodel wife?

chefjpaul · Jun 11, 2016

Paul B · Jun 11, 2016

I don't know, what is RAP?
I am doing great, not so good with my wife. The MS she has causes many problems.

chefjpaul · Jun 11, 2016

Sorry to hear, prayers with your wife snd family.

Rap, reef a palooza. The trade show in NJ.

Paul B · Jun 11, 2016

Thanks. No, I will not be going to RAP. I have never been there and Jersey is practically another country. Weekends are always booked up on my boat. (wife's health also determines what I can do)