What is this algae?


Junior Poster
Dec 9, 2007
I would like any advice you could give me on this brown dust like stuff im getting on my amazon swords and on the bogwood in my tank please.
It's only growing in the areas directly in the light and covers the leaves slowly.
Any help getting rid of it would be helpful also.


Guru Class Expert
Jul 9, 2007
Austin, TX
It's kind of hard to tell from the pictures, but it looks like brown diatom algae to me. Otocinclus fish eat this algae. I have read that it appears in new tanks and tanks with high silicates. I dont know for sure, but have read threads to that effect. I do know that it usually goes away when the tank stabilizes and that otos will really clean it up.

-Mike B-


Prolific Poster
Apr 29, 2006
Wakefield, NH
I can't really tell from that picture either. I do get some brown diatom algae growth in one of my low tech 10gal tanks that I don't add anything special for the plants to. If that is what it is. It coats the glass pretty good, but doesn't really grow on much of anything else in the tank. It also wipes of the glass pretty easy. It only builds up in that tank because I'm too lazy to wipe the glass when I do a weekly water change, otherwise no-one would ever notice it.

I have never found it in any of my other plant tanks. In that 10gal tank the substate is just ordinary P-gravel, which does have some bits of quartz in it, which I think is a silica (not certain and not a chemist or geologist, just a blonde with bad memory), so there may be something to the excess silicates mentioned.

It has not been a serious problem for me yet so I haven't done anything about it, however I am interested in seeing some more informed replies in case something changes and it does become a problem. :)


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
I won't dispute that brown diatom algae uses silicates to grow, but I'm pretty sure that all of our water supplies have considerabe silicates in it. And, ordinary pool filter sand is made up of quartz - silica. And, of course our glass aquariums are made of silica. Still, most times brown diatom algae disappears after a few weeks, even though we continue to change water, introducing more silicate. I don't know what causes it.


Guru Class Expert
Jun 8, 2007
From everything I've seen, I think it actually has more to do with unstable conditions in a newer tank than silicates. I know a lot of people have mentioned silicates, but I haven't seen any real evidence to show that water high or low in silicates has any effect on it. According to any hard evidence I've seen, for silicates to actually etch out of glass into solution, you have to have a solution with an extremely high pH (like 10). I have been able to induce brown algae just by doing a major water change and vacuuming out the gravel really well, causing the tank to re-cycle somewhat. The brown algae always goes away after the tank restabilizes. This is why I think it has more to do with some type of microorganism that does something in the tank once it's established that prevents this type of algae.