Question
I have an existing pond in an unfortunate location: under a tree. It does not currently have any fish or plants in it, except for algae. I've tried treating the pond to get rid of it, but it doesn't work. I was told by a pet store that I could put a large pleco in it to control the problem, but I'm not sure what to do first to ensure it doesn't die right away. I was told I wouldn't need a filter as long as I make weekly water changes, is this true? What do I need to do to get my problem pond ready for fish?  It is small, only 12-18 inches deep and no more than eight feet in diameter.

Answer
Nocole,

It never ceases to amaze me how much misinformation there is out there.  

There is a very simple formula for balancing a pond and getting it to clear.

NUTRIENT RICH WATER = GREEN WATER
NUTRIENT STARVED WATER = CLEAR WATER

Nutrient rich water comes from too many fish, too much fish food, spring pollen fall, excessive  rainfall, and REGULAR WATER CHANGES.  Any of these can cause your water to turn green.

Remove the nutrients by adding a layer of rock and gravel to the bottom and sides of the pond, inoculate with a good bacteria concentrate from your local pond store, and add an abundance of floating plants like water hyacinths or water lettuce.  

You also need a circulation pump that will turn the volume of your pond at least once an hour.  Pump from the bottom or from one side and introduce the water back into the pond on the opposite side, ideally in a small water fall.  

You don't really have to have a filter, but a skimmer will help keep your pump clear and make maintenance a lot easier.  It's the rock & gravel, bacteria, and plants that clear the water, not the filter.  

Now comes the hard part.  You've got it all set up correctly so it will balance.  Now you have to wait.  The water will stay clear for a few days, then it will turn green as pea soup.  About now you're saying that John don't know what he's talking about.  Well, you're halfway there.  Let it stay green. Don't change the water. Don't feed the fish.  Keep adding the bacteria concentrate.  In a few days the water will clear and this time it will stay clear.

Be patient.  This has worked thousands of times.  Yours will too.

Good Luck,

John

P.S.  Oh, and the Pleco is a good idea.  He does a good job eating algae off the rocks.  But he won't do anything for the green water.  And they can't live in cold water.  56 degrees is the magic number.  57 and they are fine.  At 56 degrees or below they die, so you have to bring them inside for the winter.