Novice needs advice on Spring maintenance

Question
Last December, I moved into a rented house, which has a small pond (approx 12x5ft, approx 4ft. deep).  The pond has about 15 carp who, according to our landlord, need no maintenance.  However, he only just acquired the house, and I am reluctant to take him on his word.
Anyway, the pond froze completely solid over the Winter, and I was very pleasantly surprised to see our fish survived when it started to melt after 2-3 months.  However, the water level has dropped about 2 ft. and there are a lot of leaves and twigs at the bottom.  I really would like to keep the fish healthy.  Is it okay to top-up the pond with tap water?  Should I clear out the debris?  Should I be adding any chemicals etc. to the pond?  I suspect the pond is about 10-15 years old, and apparently the previous tenants never fed the fish. Your advice would be greatly appreciated.
Thanks,
John, Long Island, NY

Answer
The pond is similar in size to my 1800 gallon pond as far as total volume.  Koi (carp) absolutely need maintenance as does the pond itself.  Koi experts say to have 1000 gallons for the first koi and 100 gallons for each additional, so, if you have 15 koi, it's on the high end of stocking.  My 1800 gallon pond only has two koi (but has other fish).

The pond needs care all year.  Water should be added to the pond in the winter as well as the rest of the year.  Your pond lost half its depth so you're very lucky that the fish survived.  My page on winterizing ponds is at http://www.fishpondinfo.com/winter.htm for reference for next winter.

Yes, you should add tap water.  If your tap water has chlorine or chloramine, add a dechlorinator (tap water conditioner) for ponds or aquariums per the directions.  If you're adding less than 10% of the volume, then it's probably ok to skip the dechlorinator. Chlorine burns fish's gills and can cause death.  You also should remove the debris with a net, grabbers, etc.  You should feed the koi a variety of good foods.  Right now, I'm feeding spring food and Cheerios.  I add a number of things to my pond water - pond salt, good bacteria (I use two kinds - Microbe-Lift and BZT), baking soda (because my water is very soft), Koi-Zyme in the spring to fight aeromonas (a common bacteria that attacks koi), barley straw (to fight algae), and more.  These are natural products; I don't add "medications," "algaecides," etc.  To get an idea of what I do, you can read my pond newsletters and my web site from http://www.fishpondinfo.com/pond.htm
Good luck!

Robyn