Trying something new - Walstad method and NPS filter feeder tank

[brittlestar]

Today is the beginning of a new project that I've been planning for a long time. I fell in love with the deep sea and with filter feeding inverts a long time ago and I'm finally going to make a real attempt at keeping them. The idea is essentially this: Two five gallon tanks plumbed together; one is my refugium using the Walstad method (I know that's not typically used in saltwater, but I've read her book twice and I do think it can be applied very closely), and the other is a tank for NPS corals and inverts, trying to roughly mimic the habitat found in the mesophotic zone at the outer edge of a reef or along a seamount. These are two very different environments but I think they will benefit each other for several reasons:
- A refugium is known to produce large quantities of pods, infusoria, planktonic larvae, and other organisms. In freshwater tanks this sort of thing is enhanced by the use of soil under the substrate, and in saltwater it is enhanced by miracle mud and similar products, which are effectively just topsoil. I suspect that regular soil capped with sand will be very effective. The organisms that breed in my refugium will be an important food source, especially for some more difficult/finicky corals and invertebrates.
- Nutrient export is known to be a major issue in tanks designed for NPS, and refugiums with fast growing macroalgae are known to help with that. By using a refugium roughly equal in size to the display, I hope to avoid the use of a protein skimmer that would destroy important food sources for my filter feeders.
- The fine, nutrient rich foods required by NPS will likely be relished by the organisms in the refugium, which will break them down into useful plant nutrients.
- The refugium will have a red mangrove. I know these aren't considered to be especially helpful for nutrient uptake, but surely in such a small volume of water it will be. Also, I'm going to allow the dropped leaves of the mangrove to decompose in the tank. I'm not sure why most saltwater hobbyists are so opposed to doing this, because trees always pull out and reabsorb any major nutrients before dropping a leaf (hence the change from green to yellow to brown as pigments are broken down by the plant's enzymes). Adding brown dead leaves and other botanicals is common practice in freshwater, because it doesn't contribute significantly to nutrient levels but it does a wonderful job of feeding microfauna. Now here's where I think it will directly benefit the filter feeders - decaying leaves release large quantities of dissolved organic matter and trace elements that provide a food source for corals in reefs growing near mangrove swamps.
- Macroalgaes also directly release DOC from their tissues, which I've heard is a preferred food source for sponges. I've read Dendrostein's thread where he says he finds success with Dendronephthya by feeding them blended up chaeto, so I wonder if this applies to them as well.
- The type of substrate used in the Walstad method is an effective habitat for denitrifying bacteria, but well oxygenated enough to largely avoid risks like hydrogen sulfide poisoning. With all the talk of deep sandbeds and their risks and benefits, I'm surprised that reefers don't seem to have ever tried this.
- many NPS corals from dark environments are extremely sensitive to algae growth and have no way of discouraging or removing it. A refugium will compete with microalgaes in the display to avoid this issue.
Another idea I'll be applying to this already highly experimental project is to have the refugium only exchange water with the display once or twice a day. A pump will turn on, do an automatic ~10% water change, and then shut off. This allows me to keep the two tanks at different temperatures while maintaining the benefits of plumbing them together; the refugium will be heated to a normal tropical temperature to speed up the metabolism of the plants, bacteria, and microfauna, while the display will be unheated (65-75 F depending on the season) to reduce the food requirements of the filter feeders. This will also allow me to feed only one tank so I can achieve the required density of particles in the water while minimizing the cost of having to buy expensive coral foods.
The refugium will be brightly lit with a freshwater plant light, and the display will stay as dim as possible, lit only for viewing purposes to minimize algae. I may add a biopellet reactor to create a bacterial food source for corals, but this won't help much with nutrient export in the absence of a skimmer. The refugium will have a small pump for some water flow, and the display tank will have two on timers to create bidirectional laminar flow.
I already have some appropriate macros and a feather duster that I'll be moving from another tank, and a mangrove along with some live mud is on its way. I probably won't be adding anything else to the fuge unless anyone has any ideas. The display will have some glowing marginella snails, at least one small goby (still deciding what species), and possibly some other inverts. I would really love to add a brittle star but other than the micro ones I don't know how safe it would be to keep even the smaller species with such tiny gobies. As for feeding, I've done some research and I have some ideas but ultimately I think I'll have to figure it out as I go. The tank will be fed 24/7 with a dosing pump. I am expecting to do a lot of water changes, but the refugium should help with that.
I think that pretty much covers my plan. I'll try to document this thoroughly as well as I can since it's so different from what people typically do. It probably won't work exactly the way I intend it to no matter how much research and planning I put into it, but we can all learn from it either way :)

 

[brittlestar]

Here's the start of the refugium - it's not very pretty yet :P I dug up some topsoil from outside where I know it hasn't been sprayed with anything dangerous and I'm soaking it in saltwater until more of the stuff I need gets here. It's gonna be pretty disgusting for a bit since all the microbes in it are dying from exposure to saltwater. I'll do a lot of water changes and be very careful about cycling for a couple months at least. This stage is normal in a Walstad tank.

 

[brittlestar]

Just got my dosing pump and set it up to feed my feather duster in another tank until I can move it. Got a bag of sand too but I can't use it until I get the live mud that's gonna go on top of the soil

 

[brittlestar]

So far the dirt doesn't smell bad but I'm expecting it to

 

[brittlestar]

Rereading Walstad's book - I was soaking the soil to get through the "chaos" stage a little earlier but she recommends against leaving it in water for too long unless it's in a planted tank with plenty of O2 and water flow. I'm going to try stirring it around every day and changing the water to maintain enough oxygen content to avoid fermentation, hydrogen sulfide generation, etc until I get my mud and set everything up

 

[Maxx]

Why soil instead of sand/crushed coral for substrate in the refugium?
I'm unfamiliar with the Walstad method, but it sounds like it's geared for freshwater systems?

 

[brittlestar]

The Walstad method is basically an inch of soil under a "cap" of coarse sand or fine gravel, planted very very densely. This encourages a low maintenance biodiverse ecosystem. It is geared toward freshwater, but there are plenty of saltwater plants and rooted macroalgaes in the hobby, so I'm trying to adapt it to saltwater. The idea is that the soil creates a habitat for anaerobic bacteria that do denitrification, convert micronutrients like iron into more usable forms for plant roots, and other useful stuff, while the cap creates a habitat for different bacteria that help complete the nitrogen cycle, break down organic matter, and detoxify dangerous byproducts from the anaerobic layer below. Mulm and waste can percolate down into the substrate where it's somewhat sealed off from the surface water so it doesn't pollute anything, and it eventually gets totally broken down and consumed by the plants. The activities of plant roots, which benefit from the ability of soil to actively soak up and retain nutrients (look up "cation exchange capacity"), basically solve all of the issues with deep sand beds by preventing compaction and dangerous bacteria growth while also consuming accumulated nutrients. It turns the substrate into an extremely effective and long lasting biofilter. Diana Walstad actually recommends overfeeding the tank and not doing water changes for months because more nutrients = healthier plants and bacteria = more effective and robust filtration. Soil is also a great source of carbon and trace elements, which is why it helps with growing bacteria and microfauna. No fertilizers are needed because the decomposers in the sand cap break down and sequester organic matter into the soil, which provides more than enough of every nutrient. This has been a proven and effective method in freshwater for decades and her book goes really in depth about how it all works so I'm really surprised nobody I've seen has tried it in saltwater

 

[brittlestar]

The soil also acts like a slow release fertilizer for the plants for the first few months until they exhaust its original nutrient store, which is also about how long it takes for organic matter from the tank to break down and replenish it

 

[Maxx]

I think you might have some nutrient issues going with soil vs crushed coral or sand. I say that because Marine plants have different needs than terrestrial/aquatic plants. I think you're going to end up with some serious pest algae blooms.

I hope you are successful, and I am wrong here, but I'm not optimistic.

Having said that...
The only way to know for sure is to give it a whirl and see what happens.

I'm subscribed for the results here, and genuinely wishing you success and me to be proven wrong.

 

[brittlestar]

Thanks! You're probably right but my hope is that it will stabilize itself after a few months and then become very clean and low maintenance. Walstad tanks tend to go through that process in freshwater too

 

[Subsea]

Red mangrove in 5G tank does not sound sustainable to me. However, I also like diverse filter feeders but the ones you picked are quite fragile in captive reef tanks. Good fortune on Walstad method.

Also, while some macro algae’s have holdfast, they do not absorb nutrients thru the holdfast. Only true marine plants do that and there are not very many variety.

 

[Subsea]

The Walstad method is basically an inch of soil under a "cap" of coarse sand or fine gravel, planted very very densely. This encourages a low maintenance biodiverse ecosystem. It is geared toward freshwater, but there are plenty of saltwater plants and rooted macroalgaes in the hobby, so I'm trying to adapt it to saltwater. The idea is that the soil creates a habitat for anaerobic bacteria that do denitrification, convert micronutrients like iron into more usable forms for plant roots, and other useful stuff, while the cap creates a habitat for different bacteria that help complete the nitrogen cycle, break down organic matter, and detoxify dangerous byproducts from the anaerobic layer below. Mulm and waste can percolate down into the substrate where it's somewhat sealed off from the surface water so it doesn't pollute anything, and it eventually gets totally broken down and consumed by the plants. The activities of plant roots, which benefit from the ability of soil to actively soak up and retain nutrients (look up "cation exchange capacity"), basically solve all of the issues with deep sand beds by preventing compaction and dangerous bacteria growth while also consuming accumulated nutrients. It turns the substrate into an extremely effective and long lasting biofilter. Diana Walstad actually recommends overfeeding the tank and not doing water changes for months because more nutrients = healthier plants and bacteria = more effective and robust filtration. Soil is also a great source of carbon and trace elements, which is why it helps with growing bacteria and microfauna. No fertilizers are needed because the decomposers in the sand cap break down and sequester organic matter into the soil, which provides more than enough of every nutrient. This has been a proven and effective method in freshwater for decades and her book goes really in depth about how it all works so I'm really surprised nobody I've seen has tried it in saltwater

“so I'm really surprised nobody I've seen has tried it in saltwater“

In an earlier description of Walstad method, you used the word “MULM”
Both @Paul B & I use MULM to activate the microbial loop to move carbon up the food chain. I use cryptic refugiums for that process.

"Mulm" in a reef tank

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 p...

wamas.org

“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.”

 

[brittlestar]

That does sound a bit like what I do! The biodiversity in my tanks always seems to concentrate in the mulm so I never remove it as long as there's not too much and it's all breaking down.

 

[brittlestar]

What I've read is that while most macroalgaes don't use holdfasts for much, many of the rooted siphonaceous species (caulerpa, halimeda, udotea, penicillus, etc) do use them for a significant part of their nutrient uptake. Here's a study I found about Caulerpa prolifera doing this - https://pubmed.ncbi.nlm.nih.gov/32175590/

 

[Aquadude1]

I've also wanted to try this! I'll just live vicariously through yours for a while lol

 

[Lasse]

“so I'm really surprised nobody I've seen has tried it in saltwater“

In an earlier description of Walstad method, you used the word “MULM”
Both @Paul B & I use MULM to activate the microbial loop to move carbon up the food chain. I use cryptic refugiums for that process.

"Mulm" in a reef tank

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 p...

wamas.org

“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.”

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My refugium is something like this - but I did not incorporate soil in my mix of the DSB in my refugium. However I have reverse flow through the sand bed of around 300 L/hour and I injected skimmate in the plenum below the sand bed when I started up. I inject around 24 ml 8% ethanol in the plenum every day. For the moment I add a water flow for 30 minutes each hour and if my redox is above 0 - I add ethanol. In this way I alter between aerob and anaerob environment. With other words - between reduction and oxidation.

See below ORP lower than 0 = reduction - higher than 0 = oxidation

My aquarium is a heavy loaded 300 L system and I can control my NO3 concentrations this way. I control - for the moment - my PO4 through GFO. My GFO reactor have an apartment with filter floss before the GFO in order to keep organic matter (and hence bacteria growth) away from the GFO. I have a skimmer. There is a lot of no photosynthesising but filtrating animals in my tank, sponges, yellow sun coral, small feather dusters (at places there my copper band can´t reach them) - even tunicates grow in some places. There are sediments ending up in some places - and I never clean it up. There is tones of cryptic zones in the display. I do not have Zostera (eelgrass) but I know one place there my friends have succeeded with this tricky plant in a DSB based system.

The aquarium is nearly 10 years old

If you want to use a bacteria driven system - you should maybe add a skimmer and use the skimmate in order to feed your filtrating organisms - there is no better place for bacteria growth than the skimmer cup! In order to fight one type of cyanobacteria mats I use marine snow (fine CaCO3 powder) that have been soaked in skimmate for half an hour. And my cyanobacteria mats slowly disappear.

Good luck with your experiment and keep on thinking outside the box - inside the box will always result in stagnation!

Sincerely Lasse

 

[Subsea]

Add me to this list

My refugium is something like this - but I did not incorporate soil in my mix of the DSB in my refugium. However I have reverse flow through the sand bed of around 300 L/hour and I injected skimmate in the plenum below the sand bed when I started up. I inject around 24 ml 8% ethanol in the plenum every day. For the moment I add a water flow for 30 minutes each hour and if my redox is above 0 - I add ethanol. In this way I alter between aerob and anaerob environment. With other words - between reduction and oxidation.

See below ORP lower than 0 = reduction - higher than 0 = oxidation

My aquarium is a heavy loaded 300 L system and I can control my NO3 concentrations this way. I control - for the moment - my PO4 through GFO. My GFO reactor have an apartment with filter floss before the GFO in order to keep organic matter (and hence bacteria growth) away from the GFO. I have a skimmer. There is a lot of no photosynthesising but filtrating animals in my tank, sponges, yellow sun coral, small feather dusters (at places there my copper band can´t reach them) - even tunicates grow in some places. There are sediments ending up in some places - and I never clean it up. There is tones of cryptic zones in the display. I do not have Zostera (eelgrass) but I know one place there my friends have succeeded with this tricky plant in a DSB based system.

The aquarium is nearly 10 years old

If you want to use a bacteria driven system - you should maybe add a skimmer and use the skimmate in order to feed your filtrating organisms - there is no better place for bacteria growth than the skimmer cup! In order to fight one type of cyanobacteria mats I use marine snow (fine CaCO3 powder) that have been soaked in skimmate for half an hour. And my cyanobacteria mats slowly disappear.

Good luck with your experiment and keep on thinking outside the box - inside the box will always result in stagnation!

Sincerely Lasse

Lassie,
I think it is amazing how you have quantified harnessing the natural control systems of nature.
Speaking of Nature, did you enjoy this years crayfish festival at the close of Summer? Hopefully, the russian bear doesn’t prevent life’s enjoy events.

 

[BeanAnimal]

I never clean my sump either…. Decades with of settled material.

@fishstix and others use soil in their mangrove sumps or containers thst are plumbed into their reefs.

 

[brittlestar]

Add me to this list

My refugium is something like this - but I did not incorporate soil in my mix of the DSB in my refugium. However I have reverse flow through the sand bed of around 300 L/hour and I injected skimmate in the plenum below the sand bed when I started up. I inject around 24 ml 8% ethanol in the plenum every day. For the moment I add a water flow for 30 minutes each hour and if my redox is above 0 - I add ethanol. In this way I alter between aerob and anaerob environment. With other words - between reduction and oxidation.

See below ORP lower than 0 = reduction - higher than 0 = oxidation

My aquarium is a heavy loaded 300 L system and I can control my NO3 concentrations this way. I control - for the moment - my PO4 through GFO. My GFO reactor have an apartment with filter floss before the GFO in order to keep organic matter (and hence bacteria growth) away from the GFO. I have a skimmer. There is a lot of no photosynthesising but filtrating animals in my tank, sponges, yellow sun coral, small feather dusters (at places there my copper band can´t reach them) - even tunicates grow in some places. There are sediments ending up in some places - and I never clean it up. There is tones of cryptic zones in the display. I do not have Zostera (eelgrass) but I know one place there my friends have succeeded with this tricky plant in a DSB based system.

The aquarium is nearly 10 years old

If you want to use a bacteria driven system - you should maybe add a skimmer and use the skimmate in order to feed your filtrating organisms - there is no better place for bacteria growth than the skimmer cup! In order to fight one type of cyanobacteria mats I use marine snow (fine CaCO3 powder) that have been soaked in skimmate for half an hour. And my cyanobacteria mats slowly disappear.

Good luck with your experiment and keep on thinking outside the box - inside the box will always result in stagnation!

Sincerely Lasse

That's really interesting! I love hearing about creative ways to maintain a tank. The bacteria must thrive in there. I love your skimmate idea too. I'm not sure a skimmer would be the best idea in that tank because it would pull out a lot of the other food sources, but I may try using skimmate from another tank. I imagine the gunk that gets caught in any type of mechanical filtration might work in a similar way. It might be worth experimenting to see how they differ as food sources.

 

[WildOne]

I find your idea interesting - my freshwater tank is an hybrid of walstad, hydroponics and messy leaf litter mulm.

I was looking at marginella for my own future saltwater tank, and decided that it may be risky. I found a pretty damning video on youtube, where those cute little snails murder other snails and clams.