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hi! i (as you may have gathered from my other post) have a 10g SW tank that has been up and running since last january.

it has a 1.5" bed of aragonite sand and about 10 pounds of live rock. it is currently stocked with two hermit crabs and one snail (the fish were unfortunately lost in a power outage, and i have not yet restocked).

recently, i have started getting some strange algael growth. on the sand, a thin layer of dark greenish grey algae grows (and returns quickly after cleaning), while on the walls (especially on the heater) a type that resembles the cyanobacteria seen in freshwater (thick, sheetlike, and dark green with gas bubbles) has been growing.

i test the ph, nitrite, nitrate, ammonia and salt levels regualarly and all parameters are normal. the heat is at about 82F.

when there were fish in the tank i preformed water changes of about 15% once weekly; now that the tank is pretty much uninhabited, i do about a 10% change every week and a half to two weeks. however, last week i did a very thorough clean (vaccuumed entire sand bed, shifted rocks around, 25% water change). but, the algae has already started to return.

hm... what else? oh, i don't have any corals or anenomes, so the tank is just lit with two compact flourescent blubs that i bought from a home improvement store. the lights are on a timer to come on at about 8am and go out at around 6pm. the live rocks have thick covering of purple corraline algae (which i assume is good...?)

anyhow, i hope i've given enough info to help you help me! i want to get a new fish, but i would like to figure out this problem first.

any ideas?

How much flow is there? The gooey green algae likes low water flow. It usually goes away with enough flow. Although it's likely hair algae will take it's place if the conditions are still good for algae to grow. Otherwise I'd just say to increase water changes again and see if that helps. Even without fish the critters living on the rock create some detritus along with the hermits and snails. While nitrates are low you may have something else building up in the water. Phosphates are one of the most likely and even when my tank is 0 ammonia-nitrate it still gets lots of hair algae if I don't do weekly water changes. It used to get that dark green gooey stuff all over before I added a powerhead. If all else fails it could be your source water. If you have your own system it might be time to change the filters or where your buying the water hasn't changed their filters recently.

okay thanks!

do you think it could also be that i don't have any 'sand sifters?' like, would adding a creature that stirs up the sand more help?

"the live rocks have thick covering of purple corraline algae (which i assume is good...?)"

Yep, most people treat coralline algae as a good thing because it is attractive and not a big nuisance. The only real problems it can cause are competing with corals for calcium, and growing in places where it is not wanted.

I agree about adding more flow. Decent current is appreciated by many fish and invertebrates, and it keeps the aquarium a little cleaner as well. What equipment do you have now that produces water movement, and are you open to adding something else?

Sand sifting critters will help, and are beneficial overall. Your tank isn't large enough for sand sifting starfish or gobies, though. At least, not the gobies which are really good at it like Valenciennea species. Some small snails could work, however. Nassarius and possibly cerith snails (not sure on the ceriths) are options.

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And when he gets to Heaven, to Saint Peter he will tell: "One more Marine reporting, Sir! I've served my time in Hell."

for equipment i have a power filter for a 40G aquarium, as well as a small power head positioned to blow across the sandbed. i repositioned this yesterday to point more downwards, and this seems to have helped... so far so good!

i don't have any anenomes or corals, so i don't mind the coraline algae... i think it's pretty!

the nuisance algae is growing primarily on the sand bed, and it seems to grow equally in areas of both high and low flow. so... not sure if flow is the problem...

i will try doing more frequent water changes, and plan to take a water sample to my LFS for them to test for things like potassium and some of the tests i don't have.

thanks for the help so far : )

You can try testing for phosphates(especially your source water not just the tank) but you can't test for everything. Unless you've got a few hundred dollars to spend on test kits you can't test for many of the nutrients the algae will use. Most fish stores I know don't have those tests either. In fact I only know 1 out of 4 near me that would test for phosphates. Although the test kit for it isn't too expensive if you want to buy your own. Sometimes though you just have to use the algae as your test kit. If there's too much growing and basic things like moving the equipment around doesn't help then you probably need more water changes or maybe there is some detritus stuck somewhere in the rocks that you haven't noticed.

Sand stirrers are always a good idea. They probably won't have a direct impact on that type of algae(nothing likes to eat it) but they may clean up bits of detritus that you can't and therefore indirectly lessen algae growth. Nassarius vibex would be my choice. Ceriths could work but may eventually get slightly big for a 10g. The smaller species of nass along with bubble or marginella snails if you can find them would work well. The marginellas I have are really cool and very small snails. Bright white shells that you can see across the room and they stir sand pretty well. www.floridapets.com is the only place I've seen them for sale regularly. Don't mix the name up with margarita snails which don't survive as well in most tanks.

Wise words from David Saxby, he of the monster setup with 4,000 gallons of water and 300 fish ...

Eliminate excess phosphate from day one. Controlling phosphate if you're planning to cultivate corals at ANY time (even if it is in the distant future) is even more important than controlling nitrates, because phosphates in excess encourage nuisance algal blooms that grow all over your corals and kill them off.

The trouble, of course, is that phosphates are vital to animal as well as plant life. DNA molecules are partly held together by phosphate units, so without phosphate nutrients somewhere along the line, life can't exist. In the case of vertebrates, they have an additional need to take up phosphates in quantity - bone formation. Trouble is, of course, if there are excess phosphates in the nutrient cycle - these become food for nuisance algae pretty quickly.

Fishes in particular can produce a lot of phosphates in an aquarium because the excess in their food is duly excreted. Bear in mind that, for example, the island of Nauru based its entire economy at one time on mining phosphate for plant fertilisers, because the entire island was basically a pile of phosphate rock deposited over millennia courtesy of seabird droppings! Which should give you an idea how much phosphate vertebrates can excrete when they're well fed ...

Fishes can excrete a fair amount of phosphate, particularly if they're being fed on a rich and varied diet. This of course leads to various problems with nuisance algae, which mop up both the nitrates and the phosphates. Usual control methods include products such as RowaPhos, and macroalga refugia that turn the phosphates into large amounts of plant matter.

However, by careful and balanced feeding of the resident fishes, it's possible to reduce the input of excess phosphate into the system to start with, thus giving your control measures the chance to control the levels to the point where nuisance algae can't gain a foothold. Can be a tricky balancing act with some fish species that have specialised dietary requirements, but it's possible.




Panda Catfish fan and keeper/breeder since Christmas 2002

thanks again for the words of wisdom. it's been a couple of days since my last water change, and so far so good! *fingers crossed* previously the algae had been growing back very quickly, so it seems to have slowed a bit at least. i'll do another small change in a few days when i do the rest of my tanks, too, because i suspect this may have been the problem. i guess i figured that it was silly to be doing changes on a tank with no fish in it, but that darn biology proved me wrong. haha

i'll keep you all posted : )

i just noticed that the temp in the tank was quite high (86F!) do you think this would affect the algae growth? i've turned it down since then.

Probably not. At 78F it coated everything in my tank until I increased flow and then I got hair algae until I increased water changes.

just to be clear... the algae that i am having trouble with is dark greyish-green. it grows in a relatively thin layer, primarily on the sandbed, as well as along the front of the tank "under" the sand. it does not seem to be in "sheets," nor does it have any bubbles.

(the "cyanobacteria-ish" algae that i mentioned in the very first post of this thread only grows on the heater... (?). so, i'm not as concerned with it.)

does your advice stay the same given this clarification?