Is mulm beneficial?

[Jacob Hill-Legion Aquatics]

I’ve heard that mulm is inert but then I read this on the an article: 

“Mulm is beneficial to planted aquariums because they revitalize the substrate and add nutrients for plants to consume. While mulm may look a bit unsightly, it's actually an indication that you have a thriving ecosystem in your fish tank that can support life and process organic waste without a drop in water quality”

what has your experience been? 

[Streetwise]

Mulm is a general description for anything that accumulates on the substrate, or rejoins the substrate. It is often decomposing biological matter.

My tanks enjoy it!

[Lennie]

I only let it stay in the tank I grow fry. Fry benefit from it.

Otherwise, I don't like it and clean it myself. Especially because I like bottom dwellers. I don't like the idea of my bottom dwellers constantly being inside decayed stuff sitting on the bottom of the tank. Also with every move, they make it move around the water column again.

 

[Patrick_G]

I have a two year old tank with Eco Complete substrate and it’s packed with mulm. The plants grow great and the fish seem happy. 

[nabokovfan87]

Wood pulp from clown plecos.... wonderful stuff. 

Built up poop from not cleaning, no.

Debris, other organics breaking down can be, but the main thing is to not encourage nitrates or phosphates to build up so you reduce the risk of algae.

[Flying fox 6523]

According to the people that's been in the hobby for yrs swear by it 
& if you want to get as good as they are, it doesn't hurt to learn from 
them like father fish & Cory, & L R B, & learn from doing research.

On 4/23/2023 at 3:56 PM, Jacob Hill-Legion Aquatics said:

I’ve heard that mulm is inert but then I read this on the an article: 

“Mulm is beneficial to planted aquariums because they revitalize the substrate and add nutrients for plants to consume. While mulm may look a bit unsightly, it's actually an indication that you have a thriving ecosystem in your fish tank that can support life and process organic waste without a drop in water quality”

what has your experience been? 

My experience with Mulm has been that plant's thrive on it 
better than anything else in the tank that's why I went with 
a under gravel filter system, to pull it to the roots.

[Mmiller2001]

From a high energy standpoint, mulm is an ammonia source and excess organics source. Both are the leading cause of algae and not welcome in any of my tanks. High energy or low energy.

[TOtrees]

This one of those questions that should be answered "it depends". 

There are too many variables involved to say it's always good or it's always bad. 

Here's my take on it: In an experienced aquarist's tank, a bit (or even a lot) of mulm in the substrate, or on the bottom of a bare tank, probably isn't a bad thing. But, in a newb's tank (not judging, it's just the simplest word that fits what I'm saying 🙂) it might become problematic, especially if the tank is relatively newly set up. In that new setup context it might be that the mulm (origin: poop and other organic matter) isn't getting broken down or metabolized fast enough, and it's adding ammonia to the system as it does so. Ie the rate at which ammonia is being added might exceed the tank/filter's capacity to convert it nitrates, or it's causing the nitrate level to climb into the red zone, ie up in the hundreds of ppms. Or it's releasing phosphates, leading to algae. Or or or...

Using myself as the contrasting experienced aquarist (with all the humility I can muster LOL), my tanks are well seasoned, with robust bb presence, and all the mulm is broken down into an inert form. Ie it's no longer significantly contributing to ammonia or nitrate production. It's still a great source of aufwuchs, biofilm, and microorganisms, as well as nutrients for the plants. I will say, I have a couple tanks that have very active xylivores (bn growout, and candy cane plecos), and in those yes I do periodically remove excess mulm. But I'm not fanatical about it (ie I'm quite content to let it build up, and when I remove it I'm just vac'ing the biggest piles). The tiger lotus in the tank with the candy canes, which has tons of mulm packed in the gravel, is LOVING it in there. 

[Jacob Hill-Legion Aquatics]

On 4/24/2023 at 11:42 AM, TOtrees said:

This one of those questions that should be answered "it depends". 

There are too many variables involved to say it's always good or it's always bad. 

Here's my take on it: In an experienced aquarist's tank, a bit (or even a lot) of mulm in the substrate, or on the bottom of a bare tank, probably isn't a bad thing. But, in a newb's tank (not judging, it's just the simplest word that fits what I'm saying 🙂) it might become problematic, especially if the tank is relatively newly set up. In that new setup context it might be that the mulm (origin: poop and other organic matter) isn't getting broken down or metabolized fast enough, and it's adding ammonia to the system as it does so. Ie the rate at which ammonia is being added might exceed the tank/filter's capacity to convert it nitrates, or it's causing the nitrate level to climb into the red zone, ie up in the hundreds of ppms. Or it's releasing phosphates, leading to algae. Or or or...

Using myself as the contrasting experienced aquarist (with all the humility I can muster LOL), my tanks are well seasoned, with robust bb presence, and all the mulm is broken down into an inert form. Ie it's no longer significantly contributing to ammonia or nitrate production. It's still a great source of aufwuchs, biofilm, and microorganisms, as well as nutrients for the plants. I will say, I have a couple tanks that have very active xylivores (bn growout, and candy cane plecos), and in those yes I do periodically remove excess mulm. But I'm not fanatical about it (ie I'm quite content to let it build up, and when I remove it I'm just vac'ing the biggest piles). The tiger lotus in the tank with the candy canes, which has tons of mulm packed in the gravel, is LOVING it in there. 

I am kind of a newbie because I don't have that much experience keeping with different tanks im only on my 3rd in like 4 years of keeping fish but I was wondering if I should remove the mulm when it builds up in my current tank or just gravel vac the spots with no plants? Its a 10g with normal gravel with root tabs and cryptocorynes and hornwort, super lowtech, the fish are guppies I just got so they will soon populate the tank.

Edited April 24, 2023 by Jacob Hill-Legion Aquatics

[nabokovfan87]

On 4/24/2023 at 3:54 PM, Jacob Hill-Legion Aquatics said:

I was wondering if I should remove the mulm when it builds up in my current tank or just gravel vac the spots with no plants?

In my tanks I do.  Even spots with plants I try to get the detritus off the ground, especially waste.  Some of this can be difficult, but there are techniques to clean off heavily planted tanks using a siphon + baster or other methods used to clean carpeting plants.  This is sort of when things get "bad" and you can see the affect it has on the tank and the substrate pretty clearly.  It takes a second for things to make sense and you see the darkened substrate.
 

Ultimately, in my tanks I try to clean as often as I can.  Even if it's one bucket and one small section, taking the time to do a good clean really does help to get stuff like phosphates under check and improve clarity.  As a result, your nitrates can come from the dosing you're doing and you have a better idea of what your test strips are showing.  A tank that shows 40-60 ppm nitrates with a heavy bioload might all be based around fish waste.  A 10-20ppm tank might have a small bioload and the nitrates showing are all from dosing in fertilizers.  That ratio, that balance of adding ferts and seeing the rise week to week gives you the scale of how much "nutrients" are in the water.  This is important for balancing your nutrients for your water column feeders.  Those two tanks above might both have the same amount of nutrients, whatever that 10-20 ppm of fertilizer indicates on the back of the label, but the overall health of the tank is very different given the same available nutrients.

https://aquariumbreeder.com/phosphates-in-freshwater-tanks/

[Jacob Hill-Legion Aquatics]

@nabokovfan87 thanks this really helped 🙂

 

[TOtrees]

On 4/24/2023 at 6:54 PM, Jacob Hill-Legion Aquatics said:

I was wondering if I should remove the mulm when it builds up in my current tank or just gravel vac the spots with no plants? Its a 10g with normal gravel with root tabs and cryptocorynes and hornwort, super lowtech, the fish are guppies I just got so they will soon populate the tank.

I'm going to go a bit rogue here (against the conventional or accepted wisdom)... Crypts are generally accepted to be root feeders more than water column feeders, but my own experience (with a similar or the same variety as you) has been that they respond really well to liquid fert only. This has been surprising for me. And to be clear, it's anecdotal, but hear me out. I have a shell dweller tank with gold ocellatus. Fine sand substrate, very low bioload. Plants include a few small crypts, some anubias, and a bolbitis. Until around 4 months ago, I wasn't fertilizing. This is exactly the opposite of conditions where you'd expect crypts to thrive, and this was the case with mine. Poor growth, poor color. Then I started dosing liquid fert (dry mix, applied weekly). No other changes. The improvement was instant and remarkable. New leaves were bigger, shinier and way darker. Here's a pic taken a few weeks after I started the weekly dosing (classic "tank looks so messy, sorry"); you can see the algae buildup on the old leaves, poor color, etc. Contrast that with the trio of new leaves by the sponge. Night and day. 

How does this apply to your question? If I were in your shoes (this is a suggestion, not an instruction), I'd do as you describe and vac where there aren't any plant roots, but not often and not religiously. Maybe even remove a bit of the depth of substrate, so it averages around 1" only - ie less depth of substrate = less accumulated mulm). I'd dose the water column, and trust that the crypts will get what they need from that dosing plus whatever mulm they exploit. I'd be careful with how much hornwort you keep, because in my experience it's a real nutrient hog, and it will use/steal available nutrients from the water column way faster than slower growers like your anubias. You do this by removing maybe 60-70% of the hornwort every so often, and leaving behind fewer of the bright green tips. Those are where growth occurs, and that's the part of the plant that pulls/uses the nitrogen from the water. Fewer green tips means less growth, more nutrients for the other plants. Of course there's a balancing act that comes from experience, in that you also WANT that hornwort to pull those nutrients from the water, that's part of its job.

I'd also look to add some creature that will help with mixing the mulm or substrate. Maybe a herd of cories or kuhlis, maybe chopstick or trumpet snails, etc. In my experience, this is a really valuable service because it will lift or disturb mulm near the surface of the substrate, which will find its way into your filters.