Question
We recently cemented our waterfall with morter and hydraulic cement to stop all the leaks.  And now we are experiencing alot of foam.  Limestone,and the morter created it I'm sure.  Will lava rock in the pond and/or filter neutralize the phosphorus, and eliminate the foam?  If not, what will, and will the high phosphorus harm our koi?

Answer
Not only will you get foaming, but the pH and hardness have probably gone up a lot.  You should check those.  If you added a lot of mortar and cement, it could harm the koi.  Lava rock won't get rid of the foam.  The foam is due to the limestone in the cement dissolving and not from phosphorus.  Did you test the water for phosphorus?  The best way to remove these things is to do small water changes each day or a larger change if it's really bad.  Adding activated carbon to the filter will also help to remove the various things in the pond.  High phosphorus (how high is the question?) is normally not an issue or a problem for koi but enough of anything is toxic.  Good luck!

Robyn
fishpondinfo.com