Hi Martin,
If your water is lime green, you have a bloom of unicellular algae. It can be a pain, but there are a number of of ways to deal with it.
Algae needs light and nutrients to thrive. You can reduce one or both and you should be able to control the algae. To reduce nutrients, make sure you're doing enough water changes to keep food sources at a low level. If your tank is only a week old, you're probably still cycling. That means you have levels of ammonia and/or nitrites that exceed zero ppm. (If you're not familiar with the concept of cycling, visit the newbies part of these forums and you'll see many threads on cycling and how to survive it.) In addition to liking ammonia/nitrites, algae also like phosphates. These are sometimes found in some levels in tap water, but the more common source is in pH buffers like Proper pH and similar products. If you're using one of those, you should let us know, as it will affect any suggestions. You can also reduce nutrients to the algae by cutting back on your feedings to every other day or every third day. This will also help ammonia/nitrite build up less quickly as your tanks cycles.
Reducing lights is another way to control the algae. How much lighting do you have, and how long a day is it on? Is your tank situated in such a place that it gets hit with direct sunlight for any extended period of time? That would also be super for algae production. Some people advocate a total tank blackout for 24 or 48 hours to get the algae under control.
Finally, it would help if you could find out some water parameters for us. At a minimum, we need to know pH of your tank water and a sample of tap water (after the tap water has sat out overnight). Knowing the ammonia and nitrite levels would be helpful, too. (Many pet stores will test a sample of water for you if you don't have enough $$ to buy test kits yourself.)
Hope this helps,
Jim
P.S. In case you don't know... typing messages in all caps is considered the equivalent of yelling when posting on Web forums. It's also much harder to read. Just a friendly FYI....
