Pet Information > ASK Experts > Pet Fish > Saltwater Aquarium > Grass-like growth on rocks...

Grass-like growth on rocks...

25 9:43:37

Question
QUESTION: Sorry for the novice question - just getting started with a 40g saltwater tank.  I have some small plants/creatures growing on my live rock - it looks a bit like grass but very thick grass - almost more like small tufts of shag carpet.  Any idea what this would be - good/bad/indifferent?

ANSWER: Hi Mike. No need to be sorry; that's why I am here! What you have may be one of two things. Either some form of a green hair algae or a form of macro algae. I know this doesn't really narrow it down for you but there are so many different kinds of algae out there that with out actually seeing it for myself it can be really hard to identify. With that said I will narrow it down a bit further. There are a few forms of green hair algae that can have the appearance of grass. Two of them that are common are called Enteromorpha and Chaetomorpha(although there are many others). They both are green and have a turf like appearance. They are a little thicker than other forms of hair algae. These two are considered a pest in the aquarium although the second one is very palatable to herbivores. They usually bloom in a tank that has a high phosphate level so you may want to get a phosphate test kit and check your level. If needed you can use a phosphate absorbing media to help control algae blooms. If the actual "blades" look thicker than a hair algae then what you may be seeing is a form of macro algae called caulerpa. There are many forms of this algae and they can look like tall blades of grass to little grape-like clusters. The best way to distinguish between a hair algae and caulerpa is to look at the root system. Caulerpa spreads by rhizomes meaning the root system will grow along a rock or under the gravel and new plants will be formed from the roots up. It is very quick growing, palatable to most fish and helps with your water quality. I think what you are seeing is a form of caulerpa however what kind I could not tell you with out seeing it. I hope I have given you a good place to start in identifying this algae. Any other questions please feel free to ask!

---------- FOLLOW-UP ----------

QUESTION: Jennifer,

I was wondering if you could tell with these pictures:

unknown1
http://docs.google.com/Doc?id=dcrzvf26_7fzq7fddd&invite=cpzv5tz

unknown2
http://docs.google.com/Doc?id=dcrzvf26_9fgwc3tfk&invite=sw9szq

Answer
hi there again! Wow! The pictures are a little blurry but from what I can see it looks like a form of brown alga called Dictyota. This algae, despite being considered a brown algae, can be brown, yellow, green or blue in color. They have y-shaped flattened branches and that was one of the distinguishing features I noticed from your pictures(picture unknown2). Although this form of algae is not very palatable to most herbivores, it blooms in tanks under good water conditions and has a positive effect on water quality(though it can shade or smother corals).It is considered a beneficial algae and need not be removed.