Question
We built a two tier approx 1200 gallon pond last year.  We have several small koi and gold fish in it.  Several koi have died with sores on them.  Now the pond has a huge amount of string algae. A person I live with wants to leave the algae to continue to grow until spring.  The koi do hide in it.  We do have a good pump and filter system.  Should we allow that algae to grow?  Should it be removed?  If it should be removed, what do you suggest we use to remove it?  A pool leaf strainer does not do the trick.  Any suggestions would be appreciated.

Answer
Hello Suzanne!
I think in this case the string algae problem and the Koi dying may be connected. It sounds like there is an over-abundance of nutrients in the form of ammonia and nitrites (caused by fish waste) in the pond.
These substances are toxic and will cause the fish to develop ulcers and serve as fertilizer for the algae.
The cause of this imbalance in the water has to be found and eliminated.
We have two very good and free e-books that I think will help you solve these problems. Just go to www.pondmarket.com and click on any of the "free e-books" links. Then select the "Basic Pond Care" and "Basic Fish Care" ones.
Although the e-books are short and two the point (and very helpful), the subject is a bit too complex to answer here in detail.
Please let me know if I can be of any further help.
Brigitte
www.pondmarket.com