Question
QUESTION: Hey Robyn, thank you for answering our last question! We currently have a Koi
Dome. The pond, however, has lots of algae in it. Is there an algaecide we can
get that can be used in the winter?

ANSWER: Algae normally die back in the winter unless it's still warm.  What is your water temperature?  If it's above 50 degrees F, you can do all the usual algae control stuff.  I suggest good filtration, aeration, barley straw, good bacteria, etc.  See http://www.fishpondinfo.com/plants/algae2.htm
If the pond is cold, then there shouldn't be much algae unless the nitrate is really high and/or you have certain winter-loving species of algae.  I don't suggest using chemical algaecides ever but especially if the water is below 50 degrees F.  They are taxing on all the pond life but moreso when it's cold.  What kind of algae is growing (submerged green, hair algae, suspended algae)?  Hair algae likes colder water.  Algae isn't all bad.  If your pond gets any ice/snow, then the lack of light during those times should certainly knock back the algae.  Check out my algae page for many things to try.  Good luck!

---------- FOLLOW-UP ----------

QUESTION: Our pond temp is usually around 40 degrees. The algae just seems to be getting
worse every week! There's string algae hanging from the waterfall, and there's
also hair algae in the pond. So I should just let the algae alone? I'm not sure if
our nitrate is high.

Answer
String and hair algae are often used interchangeably but there are many species of algae (I just don't know their scientific names; most people don't.)  The hair algae likes cooler weather.  As long as it's not clogging up your filter or smothering plants or other things, I would let it be.  You can physically remove some of it but it shouldn't cause too many problems.  I have watercress and water celery in my waterfall area.  It dies back here in the winter but, if your area is warmer, it may survive longer.  Those two plants grow really well and love moving water; they compete with the hair algae.  Check out my algae page for more tips on algae control.  I suggest testing your nitrate levels (as well as other things like pH, hardness, ammonia, and nitrite) at least a few times a year and certainly when there's an apparent problem.  

Happy ponding!