OK, it’s possible that I was lazy and just took a picture of my pond as it is and made it look super green with Photoshop… So sue me.

When your pond water is green (and it isn’t St. Patrick’s day) it’s most likely because of single-celled algae.

The green color comes because this kind of algae remains suspended in the water. When the conditions are right in a pond with lots of sunlight & nutrients, as many as 5 million (!) algae cells can be in each milliliter of pond water (that’s only 1/30 of an ounce).

These organisms are obviously very tiny.  They’re so tiny that they’ll go right on through even very fine filters.

The trick is to use a flocculant to help filter them out. Flocculants make the small particles stick together so that they’re large enough to be caught in the filter. I really like the new Rapid Clear fine filter pads. They’re a disposable filter from Aquascape made to be used with a flocculant.

Be careful, your filter pads will clog pretty fast. When I use a flocculant I also like to use a sludge and filter cleaner, too.  The bacteria in the sludge cleaner tracks down those chunks of algae and eats them.

Once things are back under control, I keep them that way with a regular use of beneficial bacteria (the dry is what I recommend for regular maintenance since it is the best bang for your buck).