Parasite? Do I have one.

Question
I am have a few fish tanks set up and they only have guppies in them, I noticed the other day that there were these teny tiny little white things on the glass and they move but you have to look really close to see them move there are like 100 of them. Do you know what it is? And Will it harm my guppies? And last how do I get rid of it? Thanks for all your help.

Answer
Hi Jessica
The more common little white things like that in a fish tank are either planaria, which looks like a small slug(snail with no shell), usually a whitish color, and has an arrow shaped head.  Usually you'll see them crawling on the glass.  They're harmless for the most part, but some will eat fish eggs or small fry.

The other, is nematodes.  They look like small, thin, whitish, worms.  When they swim, they look like an S.  You'll see them on the glass(sometimes they look like hair on the glass), or swimming in the water-especially after doing a water change or distubring the gravel/substrate.  These guys are also harmless.

Both kinds usually show up in tanks where the fish are being overfed, and/or not enough water changes/gravel vacuums are being done.  Best way to get rid of them is to cut back on feedings, feed once a day what the fish will eat in about 4-5 minutes.  Scoop out any uneaten food.  And, be sure to do weekly water changes, and vacuum the gravel really really good.  Even skip a day or so during the week.  The guppies are probably eating them as well.  I know I've seen my platy fry eating them. Between those 2 things though, it reduces the food available for them, and hopefully they'll die off.  

Also, I had this problem with one of my tanks, using the same equipment will transfer them to other tanks :)  I now have them in almost all my tanks.  So, it may have started in one, but they do spread fairly easily....again though, they're harmless.

Hope that helps.

Christy