What kind of filter are you using? If it is a homemade bio filter then it will go green before it clears up because it has to get the bacteria established before it will start doing what it is suppose to do. Don't worry it will start working before you know it, you will go out one day & it will clear up just over night. Don't give up on it!! I personally don't like using algae killer because while it kills the algae & it dies it just feeds new algae blooms which then just restarts the cycle over again. You could try putting some non-scented non-clumping cheap kitty litter in your pond to help control algae on surfaces.