Eric Borneman on Reeffrontiers:
"....the thing about algae is, as I think I mentioned, there is a nutrient component and an algae component. Algae, being fully autotrophic, will thrive in very low nutrients if there is no grazing. The reason they don't take over even oligotrophic reefs is the grazing pressure. Obviously, higher dissolved nutrients helps them grow faster - and in excess makes corals fare peooer - but algae almost always grow faster and outcompete corals were in not for grazing. Turfs are highly grazed, macroalgae less grazed and also depedning on how palatable they are and what other algae are present.
Fish tend to be most finicky, especially if they know there is food coming (like in tanks). many urchins are great unfinicky generalist grazers - even though if offered turfs or Dictyota, they will graze turfs first, they will eat Dictyota when there is nothing else left. A fish in a tank will probably think "screw the Dictyota, a lettuce clip will be along soon enough". Snails work, but nowhere near to the eficiency of urchins, and snails may not graze some algae, or they can lierally be killed by it. Some of the brown algae are very toxic, and urchins can detoxify them somewhat - as can some fish. I am not aware of snails that can do this.
Anyway, those types of organsims, including lettuce slugs, etc, are macrograzers. A large portion of grazing belongs to the micrograzers - basically amphipods. If you poke through a Derbesia patch, you'll see tons of amphipods. The idea here is to let the macrograzers do their work on the big unpalatable and out-in-the open areas and reduce the load on the amphipods who will take care of little new sprouts., stuff in the nooks and crannies, etc.
As to rock crevices being filled with detritus or purportedly acting as a nutrient "sponge" that leaches out nutrients, I don't really go for that idea. It's possble, but I think it is rare, esepcially if the carbonate source is not from some polluted coastal area. The porewater of rocks is loaded with critters and microbes that easily should be able to manage any organic deposits over time. They cycle....lots of detritus, low bugs leads to increase of bugs then decrease of detritus, then die off of bugs, and repeat. As for the idea of carbonate acting as a time-release capsule for dissolved nutrients, same thing - the life in the rock should handle it easily, and if the water is that nutrient laden, and the rock is also laden, and the water is changed to a pure form, and the nutrients seep out through porewater, it won't take that long in reef rock because of the porosity and small size of rock. Turnover time, by necessity if in low nutrient water and without any life present in the rock at all cannot exceed the length of time it took to get that way in the first place. Any leaching, provided it is not by solid material containing harmful elements being slowly dissolved, should be pretty quick.
Finally, I have spent a lot of time taking both live rock and dead coral skeleton and decalcifying it (using acidified EDTA). The amount of algae, worms and sponge in marine carbonate is ridiculous. Sometimes I think there is more sponge than carbonate. So, nutrient leaching could also just as easily come from the die-off, excretion and boring action of all these organisms. If you put a piece of live rock in a bare bottom tank and wait, you'll get a pile of detritus really fast. Where do you think this comes from? The surface? Well, a little from algal shedding and surface material and mucus, but the majority comes from borings and waste of those things inside the rock and released out the pores. Live rock is a very active thing, and the notion that it is a big carbonate sponge that sucks up all the nutrients and slowly releases them causing algae and/or posioning the tank I think is relatively rare. Porewater is greatly higher, normally, in N and P, and is largely oxidized or absorbed before it enters seawater. That aspect of it is what makes it functional and able to support the great amount of life in it.
Sometime when I decalcify some substrate, I'll take a photo of the substrate and the material left after decal....its really amazing. I'm not saying that it never happens, or that a mismanaged tank could not produce these results, but if the tankis mismanaged to that extent, those issues need to be addressed before one starts throwing out the sand or rock thinking its going to fix an algae problem. I can assure you that even a cesspool of a tank in the presence of leaching substrates and gross food inputs will have no visible algae in the presence of enough grazers. Not suggesting this, just making a point. "
, WATER CHANGE, WATER CHANGE, WATER CHANGE!!!! Reminds me of the movie "Animal House".
