Problem worms?

[chester]

:?:

I have noticed a large amount of small @3 mm blobs,flat,rusty colour covering my rock and sand.Originally I think I had a a few on a piece of rock but now on closer inspection they appear to be covering most rock and some sand.Apart from being unsightly are these a problem and is there anything I can do to get rid of them?

 

[Anonymous]

They sound like photosythetic flatworms. If that is indeed what they are, they are not likely to harm anything, but they can develop into large, unsightly populations. Do a search here with the words "red Flatworms" and you will find a bevy of things to try and control them, although few if any work well.