Macroalgae Nano

Donya · Sep 18, 2026

I've always had macroalgae in my marine tanks up until very recently. I have two well-established marine tanks right now, a reef nano and an anemone/urchin nano. The reef had flourishing Caulerpa prolifera for years until the fauna shifted this summer and coralline outcompeted it rather fast. I salvaged a few scraps of the prolifera and tried to protect them in a breeder box-like container in my urchin tank while I figured something out...well, that little container is now known as "the snack box," and I find myself without macroalgae for the first time in about 20 years. When my husband heard my darth-vader-like "noooooooooo" at finding the last of my macroalgae consumed, he said "guess you'll have to set up a seaweed tank then" and then when I saw 10g tanks were half off, he said "get two" lol.

So here we go. This is going to be a properly new venture for me in marine tanks since I've decided I'm not just going to do the same old same old I've always done of just using macro for nutrient export in a different type of tank. This time I'm going full planted marine tank mode and try to make this like a coastal tide pool. I've got a horticultural LED and reused a spare heat lamp stand to have it hang over the tank. If the particular bulb doesn't blast enough, I can easily step up to a more powerful one within the same fixture. This build is particularly exciting for me because it's my first new tank in over a decade.

I'm going to try my hand at cutting my own acrylic top/lid this weekend. The power strip will be going elsewhere to free up the lower shelf. Not sure yet what I will put on that shelf; it's meant as a double-decker for aquariums. I can either put the 2nd 10gal there with a more standard LED strip (I have plenty of spares), or I have two ancient Fluval Spec III tanks sitting on a shelf that would fit side by side. Or I could have a Fluval Spec on one side and my phytoplankton culturing operation on the other so I don't have glowing green bottles on my windowsil creeping out anyone who pulls up my driveway. For now though, time to mix up some more saltwater, get this tank filled, and source some new macroalgae species.

Back in the fold · Sep 19, 2026

I know nothing at all whatsoever about marine set ups but I do enjoy reading about them . Who knows , maybe I’ll pick up something that could be useful in my little system .

Donya · Sep 20, 2026

Aaaaaaaaaaaand I bodged the DIY lid.

I don't know what I expected the outcome to be, having never cut acrylic before and having left myself exactly one fail-cut worth of error before it would become too small. Guess how many fails there were lol yes, exactly one too many. I will have to go get another sheet at some point and try again. For now, I salvaged what I could with neat edges and it does serve as a splash guard for the fixture, so I will keep it there. What I have learned and will apply to my next attempt: the multitude of tutorials I saw showing breaking the scored edge downward over a table edge, just holding it with in place leaning on it with a hand...utter rubbish with the material I have! The sheets I can get locally flex in very weird ways anywhere my arm can't hold it downand breaks chaotically even with a really deep score. The strategy that ultimately gave me two pristine edges was flipping the piece upside down after scoring, setting a hefty straight edge piece of wood just a couple millimeters behind the joint, putting my whole body weight on that board, and then pulling the free edge UP. Tada, two beautiful clean breaks. Just...not enough material left at that point for what I intended. I do have some worry that the material is SO flexible that my original lid shape plan may be a sagging risk over time. I was going to leave a strip open down the left side and just have it supported on 3 edges; I may need to 3d print a brace for that end or just do a notch instead. I don't think I want to get thicker material...the next step up in thickness seemed like overkill.

I have a shipment of macroalgae coming by mail later this week. That may seem rushed given the sand dust is only just settling, but my goal is to get the macro there before the rest of the biological filtration gets too established, so that the macro can more easily become the dominant nutrient exporter with minimal competition. I want other stuff to have to compete with the macro to get going, not the other way around. There will be a potential risk of stuff trying to grow on the macro once it's in - but IME that would still be a big problem in an established tank where a more diverse ecosystem is present and a small bit of macro is the newcomer. I may still need to add a small UVC to help beat back microalgaes and other film-forming organisms as the macro establishes; not sure yet.

Donya · Sep 24, 2026

Fist macro additions arrived and went in today. These are dragon's breath (Halymenia?), some kind of Gracilaria, Codium, and sea lettuce (Ulva). Now time to see what takes...out of 4 species, hopefully at least one does. I have never kept any of these. I'm most optimistic about the dragon's breath and least optimistic about the Codium. All species seemed too fragile or slippery to try gluing or attaching with rubber bands, so I have just gently nestled them into the top layer of sand and rested some dry rock meant for coral frags over top of that to try to stop them from floating away. Tank is a bit cloudy because of me shifting the sand around in that process.

I also got a bottle of pods that I was going to dump in, but they were shipped in obvious green water...which feeds the pods so that's cool, but it means I can't risk putting it in my macro tank as a fauna kick-off. I need the macro to get quite established before I risk introducing phyto without a UV clarifier in there. So I guess I dump the pods in my reef and/or urchin tank and hope some of them don't get eaten immediately.

Donya · Sep 25, 2026

The game is finally afoot!

My first challenger challenger arrives: diatoms - the little brown patches on the top of the sand. Interesting that no blooms at all happened until the macro went in. I was lighting the tank 16h/day the whole time it was macro-less, essentially trying to trigger these kinds of blooms to get them over and done with, but nothing happened until now. The diatoms must have only arrived with the macro. These days, the vast majority of live rock in the hobby never touches real ocean water...I wonder if the same is true for live sand now, cultured from dry, dead sand with bacteria additives. All live sand I've used in the distant past produced diatom and sometimes cyano blooms within a few days of getting water and light on it.

There is also a second challenger: epiphytic growth on the Gracilaria. Not enormously pleased with this one. It did definitely arrive with the macro; kinda saw it when opening up the bag.

But I am not without my own champions to throw in the ring. Time to release the bottle of Munnid Isopods. :hey:

(EDIT: the Isopods did NOT come in green water unlike the copepods which are now in my other tanks)

Donya · Sep 26, 2026

I've gotten the DIY lid situation sorted out. I did end up going thicker on the acrylic since I realized I actually do need to keep a small gap at both ends. A chilly day today shows the condensation that gets going. If I block up one end completely, it gets very drippy on the closed side, and I don't really want water building up badly at the rim. Still a bit foggy with the double small gap when it's cold in the room, but not interferring with the light or being drippy. Going for 1/4in acrylic made the snapping at the score mark step kind of terrifying, but the advantage is now it won't sag when just supported on two edges.

So far the ogo Gracilaria is in the lead for new growth despite the epiphytic invader and being on the side. There's been about 1/4in new growth per end yesterday and today. I'm seeing some smaller growth in the dragon's breath and Codium, can't tell any change on the Ulva.

All of these macro species are supposedly edible (although I'm perplexed by that with Codium, given how simultaneously slimy and hairy it is). Since my macro tank is going to be a tank full of potenitally edible things, I decided to set up the other 10gal as the lower tier tank and grow a different kind of edible thing. The lower 10g will be FW with the goal of growing Azolla for my chickens. This may be the only mention that 2nd setup gets here, since it's going to be FW, but at any rate those are the plans for my macro tank's downstairs neighbor. Although not with that particular old strip light I dug out of storage...I don't think I can deal with this degree of dueling Kelvin ratings so close together.

Donya · Oct 1, 2026

Diatoms have vanished. Macroalgae growth still going strong, espeically the ogo Gracilaria. No other algaes getting going. No detectable nutrients. Stuff is getting used up and the macro is dominating the uptake despite a small amount of epiphytic growth here and there.

Regular plants give you some warning when they start to run out of something they need: leaves turning colors, getting wily, etc. My past experience has been that once Macro starts showing you any analog of those signs, you're way too late. So...I don't dare wait for any of that and it's time to get some nutrient sources being added regularly. I'm approaching this in two ways: dosing ChaetoGro and adding carnivores that won't harm the macro. My carnivores currently are two species of whelks: Babylonia and Nassarius. There are a couple Babylonia and more of the smaller Nassarius. These guys readily eat carnivore foods meant for fish and other marine animals, and the Babylonia can be pretty messy about it. They dig in the sand bed, which also means I get the sand turned regularly to stop it compacting and getting unwanted stuff growing on the surface.

One of the Nassarius:

One of the Babylonia showing off its elephant-like snoot eating a carnivore pellet.

It's possible the Babylonia may become too bombastic for the tank as htey grow; if they do I will swap them with another species of Nassarius I already have in my anemone/urchin tank.

Jennet · Oct 1, 2026

Eeeek - snails. I was beginning to like watching this. Oh well, as long as I am only watching it I suppose I'll cope. Very interesting.

Donya · Oct 1, 2026

Jennet said:
Eeeek - snails. I was beginning to like watching this. Oh well, as long as I am only watching it I suppose I'll cope. Very interesting.

What's wrong with snails?

I've always thought Babylonia and Tonga Nassarius have beautiful shells. Most marine tanks have one or more species of snails, and various whelks are pretty typical. This tank is very likely going to stay invert-only, so some combo of snails/crabs/shrimp...but options in crabs/shrimp categories that won't risk damaging the macro are pretty sparse.

Jennet · Oct 1, 2026

I have no problem at all with snails in the garden, or even in someone's aquarium, as long as it is not mine. It is just the thought of them touching my hands when I have to do maintenance in the tank. Not quite as bad as my fear of spiders. Fine to watch where I can control the surroundings, but not to touch I'm afraid.

Donya · Oct 19, 2026

Forgot to update this for a while - the macro nano development continues! There have been a lot of new additions, so things are kind of messy right now as I wait to see what grows in well. There will be some algae-scaping in the near future to neaten things up.

How the first-in macro species are doing, more-or-less to my initial expectations:

Dragon's breath (leafy red stuff) is doing great, lots of new growth
Gracilaria (noodly red stuff) is doing great, lots of new growth
Codium is showing very very very slow growth. Still not sure about this one's long-term viability. It may eventually get out-competed.
Ulva / sea lettuce is probably going to have to be yoinked out. Large portions of it definitely are NOT growing even though they are surviving. Parts that are just surviving are getting significant epiphytic growth, so I expect they'll eventually start to melt.

Things that have changed or been added:

I started to get microalgaes going on the glass and rock, although it's well under control now because....
I added a couple Trochus from my reef to graze on the microalgae
Added button snails - never kept these before; I've read they are a short-lived species that can reproduce in an aquarium provided nothing eats the hatchlings.
Added zigzag periwinkles - truly tiny snails that can get in the nooks to eat things bigger species can't reach.
Added sexy shrimp - they are helping clean epiphytic growth, which is now decreasing on the Gracilaria.
Added two Caulerpa species, one of which is new to me. Basically I wanted to keep some green things in there if I yoink the sea lettuce and if the codium bites it. These are already growing well. I will have to be aggressive in trimming them.
Added a pencil cap macro - never kept one before. It's a slow-growing calcareous macro species.
I have some bizarre growth occurring on snail slime trails in the sand of all things. I will need to stick it under the microscope; can't tell if it's a weird type of microalgae, cyano, or dinoflagellates...I've never actually seen anything with the particular color/texture combination before and I've seen a lot of stuff. Whatever it is, various critters are eating it, so I doubt it will persist as the tank matures.

Also forgot to list what all equipment I'm running this tank with other than using a horticultural light.

Sicce shark nano internal filter - love that there are finally magnet mount things like this.
Imagitarium small internal filter - just an excuse to be able to run carbon if I need it and break up surface scum with minimal bubbles.
50W heater
Red a weak 24/7 LED bar (upper right) - new addition to try to make the daily on/off of the horticultural light less drastic on the fauna. Blue is the norm for moonlights on reef tanks, but it can also encourage microalgaes, whereas red is more commonly used for macroalgae refugiums.