Question about diatoms

J

JMac

AC Members
Jan 2, 2005
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What are they and what causes them? I have a 55 gal. and a 29 gal. in the same room. The 55 gallon gets a lot of black, or dark green, dots on it. I found a site that says they are diatoms. The 29 gal. doesn't get them at all. They are a devil to scrape off, but look awful if I don't. I have a pleco in there, but he doesn't touch them. Is something going on with the water in that tank that's causing them? It's been set up for several years and I do water changes every week. thanks
 
Thanks for your quick response. I did go to the brown algae site, but it seems that brown algae is in saltwater tanks. I guess I should have said this is a fresh water one. This is black or very dark green dots. What else could they be?
 
diatoms are not only in marine tanks .. in fact, this is a very common freshwater occurence. what you've got sounds like 'spot' algae. again, Google is your friend.
 
Sounds like it could be nuisance algae or even freshwater cynobacteria(which is a PITA to get rid of). Nuisance algae is just something that shows up when something in the aquarium is out of balance. Possibly overfeeding or too much light. How long do you leave the lights on for and what kind of lighting do you have? How much do you feed and how often? What is your water change schedule like? Algae needs a light source and nutrient rich water in order to grow. Cutting down on the light schedule as well as the feedings and upping the water changes will help if it is just algae. If it is freshwater cynobacteris then light is a major source for this as well as too many nutrients in the water. Again lighting and feeding factor into this kind of problem. I am battling freshwater cynobacteria in two of my aquariums and in one of them it had gotton completely out of hand. After trying every natural method I could think of, I have finally resorted to a five day blackout. I killed the lights last Saturday and covered the entire tank with garbage bags to make sure no light could get in the aquarium. I did a water change first though before doing this. No food and no light for five days. The unveiling was this morning when I uncovered the tank to see if it worked. I think about 75% of this yucky cynobacteria is now dead but there still is some in the aquarium. Now I have to think of what else I am going to do to get rid of the rest of it. I sure hope this is not what you are seeing in your tank. I am about ready to pull my hair out with it. Maybe you can post some pictures of this stuff so we can get a better handle on it and try to identify it for you.

Marinemom
 
Thanks everyone. Very helpful info. I checked the links, and now think it is simply green spot algae. The lights are on probably 12 hrs. most days. Too long I suppose. Don't think I over feed but maybe I do. It puzzles me why the 29 doesn't get this stuff, and there isn't even a pleco in it. Maybe my guy isn't doing his job. Marinemom, I hope you get your problem cleared up soon. I've not heard of cynobacteria before, but will do a search for it. I haven't visited this site for ages, don't know why. It is a great place with lots of knowledgeable people here.
 
Also cynobacteria comes off easily and is very slimey to the touch. I think you are having a run with nuisance algae. Twelve hours a day for the lights is too long unless it is a planted tank. I would cut the amount of time that the lights are on and see if that helps.

Marinemom
 
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