Murky water corals


New member

I'm planning a lagoonal segrass dominated tank with a small reef. I looking for coral species that will do well with abit more nutrients and help out with particle filtration. I'd like to experiment and run the tank skimmerless using alot of filterers to deal with particles and segrass/macros to export inorganic nutrients. "Murky water" acropora was mentioned in your RK article "Renaming our corals". Are there any such species commonly accessible to reef aquarist? Do you think the setup in general is plausible?
thanks in advance for any help!!

P.S. Discussing the setup in this thread as well:
I'll say that I really like your ideas and planning, but that this subject can be a bit more complex than perhaps what you've realized or than what one could glean from my article.

For instance, what exactly one means by "murky water" or "lagoon" can vary widely and is important in determining which species can grow in a place.

For instance, some areas with turbid (=murky) water have only a few meters of visibility due to a lot of suspended colloidal material in the water from a river. Think of a muddy river emptying into a bay. Some corals thrive here while others don't tolerate the conditions at all. This is true even within the genus Acropora. Most Acropora won't deal with the sediment, but here and there some species will do just fine. I've seen various bottlebrush species and a few corymbose (e.g. A. millepora) in such conditions and they appeared to be just fine. Montipora, Galaxea, Hydnophora, various mussids, Porites, etc. would be more likely to dominate these areas than Acropora. Mostly what is controlling this dominance is a coral's ability to shed sediment via mucus, etc. Corals that are good at getting rid of sediment easily outcompete those that aren't good at shedding sediment. Most Acropora aren't good at this (though a few seem to be) which is why they tend not to be dominant here.

On the other hand, some lagoons have crystal-clear water similar to what is on the outer reef and many Acropora spp. are very, very common. In fact, usually one sees big stands of staghorn Acropora (they DO NOT grow on reef crests, not sure why people insist they do) in lagoons with clear water. There is a huge variety of corals that will grow in a lagoon like that though. The water is clear and the light is bright in the shallows, but there is protection from storms, etc.

Also critically important is the degree of water motion in a lagoon. This can vary markedly and is a very important control on species abundance. In a lagoon where the water flow is very sedate the dominant group of corals will probably be Porites spp. If the water flow is strong (for a lagoon) we'll see domination by branching Acropora. In between those two and faviids/mussids become the dominant groups. This has to do with physical features of the lagoon, tidal currents, etc.

As for nutrient levels in a lagoon vs. an outer reef, this is mostly determined by where the inputs are coming from. If a river is flowing into a lagoon it is going to impart a lot of organic material. The water may still be relatively clear (though not as clear as further from land) but there will be more particulate material. It is important to note that while this lagoon is usually considered to be more nutrient-rich than the reef slope away from land, this is mostly due to a greater amount of particulate material/plankton in the water column, not so much due to elevated DIN and DIP, though those can be slightly higher as well. In general the DIP concentration in a lagoon is about the same as in a very 'nutrient-poor' reef slope. The DIN concentration tends to be very slightly higher, in general, but still much below a "0" reading on a hobbyist test kit. Also, getting the amount of particulate material into tank water as compared to what's normal in nature usually proves tricky.

So I guess my suggestion would be to think of the species composition and what will thrive in the tank being controlled less by nutrient availability, as this usually is not very important in nature--there is usually enough particulate material anywhere for the majority (though not the entirety) of coral species to survive). What will really be controlling what can live in the tank, which parallels the controls in nature, are light intensity and water flow strength.

For a lagoonal tank it wouldn't make much sense to include a digitate Acropora as it would be very rare to see optimal water flow for this coral in a lagoon. When they (rarely) grow there they usually assume a very thin growth form and my guess would be that they do not do nearly as well as elsewhere on the reef (reef flat, upper reef slope). On the other hand, it would make a lot of sense to include staghorn Acropora, or some of the digitate and plating Montipora, or Porites, or Hydnorphora, etc. because those would all naturally be found in a lagoon (more water flow for the Acropora, less for the Porites, most others in the middle).

So, to get back to your questions a bit more directly, yes I think this tank is very plausible (I've had the pleasure to see tanks like this several times actually and they work quite well) and a good idea. I'd keep corals like those mentioned above--plating and digitate Montipora, Hydnophora, Fungia, Porites, Favia, Goniastrea, Lobophyllia, Symphyllia, Galaxea, maybe Trachyphyllia (depending on light intensity), etc. Acropora should do well in higher flow spots, especially if they have thinner branches. Bottlebrush species should be fine as should many corymbose and bushy species. Staghorn species, especially with thinner branches, should be fine too. There are other corals still. There are a ton of zoanthids, mushroom polyps, soft corals, anemones, etc. that could go in tank like this too. I would not recommend mixing all of the corals I've mentioned above, but this should give you an idea of what is naturalistic and likely to work well for you.

If you have any other questions feel free to ask.


Hi Chris

Thank you for your swift and detailed answer! For my tank I have only two fixed parameters so far. I't will be seagrass and macro dominated and I will use a
two-way surgedevice. The latter is my own design so the tank will be part "tech-test". I have many choices when it comes to corals, feeding regiment,
circulation apart from the surge, lighting etc.

I was initially thinking about recycling tank waste as food for filterers. I've havent though about a technical solution as of yet but the basic idea is to collect particles from the water with a filter and feed it to the filterfeeders a few times per day. Do you think corals can make use of such material?

Do you have any links or references to similar tanks?

I don't have the time right now to review the corals you suggested in detail but when I do I will probably have more questions!
Thanks again for your time

The one real suggestion I'd make is that it is not necessary, and probably counterproductive, to use a filter to remove particles from the water and then try to feed that to the corals. Doing nothing at all will work much more effectively. You'll have a nice sand bed (presumably) where there is a lot of infauna and meiofauna (little creatures) constantly processing any organic material that hits the bottom. Some of this will get resuspended as detritus and feed your corals and some of it will become plankters and feed your corals. They will catch this material just fine without your intervention (they do in nature afterall ;) ). In fact, as I see it trying to filter this material out of the water and then put in back in the water to feed them won't provide any benefit and will create a lot of unnecessary work. Not only this, much of it is likely to begin breaking down beforehand. This may or may not affect the quality of what you're feeding. Not only this, but there are many, many other interesting suspension feeders that you probably won't or won't be able to target feed.

I'd set the tank up, feed it, probably use activated carbon, supplement Ca and CO3, do water changes here and there, and watch things grow. I wouldn't do much else. As discussed, using a skimmer is up to you. I've seen great tanks with and without skimmers.

Unfortunately I don't have any links handy to show examples. Eric Borneman used to have a nice seagrass/patch reef tank. I've seen examples at various public aquariums as well and a few here and there over the years. I'd very much like to set up a tank like this one day (a mangrove tank too--mangrove communities fascinate me) though I haven't had a chance yet and probably won't for a while due to time constraints with school. Actually, with how busy I usually am I'm amazed anything survives in my poor, neglected tank ;)


Hi again,

The more I research for this tank the more people are saying "Leave it as it is". The LR/LS fauna will of course adapt to the tank and the filterers will, as you say, do better without interference from me.

For supplements, do you mean CaCO3 or Ca and NO3? After reading som threads over at the plants and macroalgae forum I plan to use Ca(NO3)2 as extra NO3 source if the tank should need more Ca than from kalkwasser. When the tank is stable I might se if I can skip the Kalkwasser altogether and just use Ca(NO3)2 for Ca.

Thanks again!
You have to have a source of alkalinity added to the tank. The organisms use carbonate alkalinity as they calcify. Ca(NO3)2 adds no alkalinity to the tank. This will not work as a cal/alk supplement. Kalkwasser should work fine. If you need more supplementation beyond what kalk can provide I'd probably use a 2 or 3 part additive (e.g. Randy Holmes-Farley's homemade recipe).

These are Eric Borneman's old seagrass tank. Check it out. Very well done, and very realistic.


Hi again,

I had some thoughts on alk trying to get away from using CaCO3 since I dont like mucking about with nasty chemicals. The idea was do use NaHCO3 or Na2CO3 instead, but it's probably best to stick with kalk and limit experimenting to one area at a time. :)

Thanks for the links. Looks really cool! Is that a coral down among the grass and macros?

Thanks again

Yeah, many different ways to provide Ca and CO3 that work just fine. Kalkwasser is effective, especially for systems with lower demands (often not enough with lots of calcifying organisms).

Lots of corals in those tanks. He had a Catalaphyllia in there, Pectinia, Zoanthids, etc. Lots of lagoonal or inshore corals.

Hi again Chris,

Thanks for all your time so far! I must admit that this "deeper" dive into coral species is abit difficult for me. There's just so many of them. When reading up on coral families, i.e. acroporididae, pocilliporidae etc, I came across the fact that different families extend their polyps at different times of day and for different durations. Acording to my sources most, but not all, acroporidae only extend their polyps at night while most, but not all, pocilliporidae do it around the clock.

Apparently acroporidae do well in high flow turbid waters in the wild so for the corals themselfs, regarding them as individuals in the wild, this does not seem to make much of a difference. In a tank however where there is a high frequency of nutritious particles I wonder if this might be an issue. Do you think selecting species with longer polyp extending time is a better choice? The other choice I suppose is to mix the two categories. My logic for the first choice would be that the total filter surface time over the course of a day would be better at removing particulate nutrients from the water.

Thanks again for all your help
Hmmm, I would say you're almost stepping into the realm of overthinking things at this point ;_ You want to have an inshore/lagoonal/seagrass and patchreef tank: learn about the species that would naturally grow there and concentrate on those. Usually most species in the family acroporaidae tend to extend their polyps only at night, but that is true of most corals. Most Montipora (there are 4 genera in the family, Montipora, Acropora, Astreopora, and Anacropora) tend to extend their polyps continuously. A lot of poccilloporids will extend their polyps continuously, but that shows a lot more variablity between species for seemingly unknown reasons. Also, most corals in captivity seem to extend their polyps continuously even if they don't in nature. Again, this happens for unknown reasons.

Also, a lot of the particulates and detritus that many corals eat they capture with mucus and transport to their oral openings with cilia. Thus, the polyps don't necessarily need to be extended for the corals to feed (look at the agaricids and pavonidae) on pseudoplankton, though they do catch a lot of larger particles and zooplankton with the polyps.

I would focus your time on learning about the natural habitats of these animals though. You'd be much better served by learning that Porites cylindrica is often a lagoonal coral and that Acropora hyacinthus is not than to debate the merits of the acroporidae vs. poritidae in their effectivness at capturing detritus ;)

Hi Chris,

Overthinking? Me? Never happened before!!!.. In denial? Who me? :)

Well, logic has is't boundaries. How well the individual species do in a lagoonal biotope is the primary base for selection then!

Thanks again Chris