Yeak ! Worms in my tank !

Hello there,
I'm a new reader of the list and i'm from germany.
The worst problem in my 100 cm (160 litre) tank are some ugly worms creeping
around. Although cleaning my plants everytime i buy some the worms must have
come along with them. My local pet-shop-keeper gave me a fluid from - i think -
TETRA. I tried it several times but after some days the worms started creeping
Here's a describtion of the worms :
- color  : white
- length : max. ~2.5 - 3 cm (1")
They are on the cover plate of my tank and if i stop my filter they swim in
the water. After several minutes they stick to the glass of my tank and start
leaving the water. Sweeping hundreds away brings the next time thousands of
them back.
A friend of mine has the same problem - without stopping it yet !

I would be very glad if somebody could help me. 

Another question : What does DIY mean ? Is it the name of a company ?

**  Lars Rusdorf           email : Lars.Rusdorf at Informatik_FH-Fulda.de **
**  Stresemannstr. 31                                                  **
**  36039  Fulda - Germany                                             **