Hi. I love your site! What can I do to raise the pH in my pond? This is my first experience having koi and the pond with the red cap orandas I had last year did not ever get so low.
Also, my largest, fastest koi disappeared overnight. I was shocked as I thought he was uncatchable! I have also lost 3 red comets. My pond is covered with an arbor, so I suspect it might not be a bird.
Thanks!
Barbara

The easiest way to raise the pH is to add some baking soda. You'll have to add just some at a time, wait a few days, check the pH, and repeat as needed. Even as a chemist, a pond is too complex to just measure the amount needed. If you want to spend more, you can buy pH up solution which is probably sodium hydroxide which is a stronger base.

What is the pH of your pond? What is the pH from the tap? How big is the pond? Is there a lot of algae? Algae or a lot of other plants can result in pH swings during the day. Check the pH at dawn and dusk. Are they the same? Lots of debris can also cause pH swings. Baking soda raises the pH (unless it's over 11 in which case it lowers it) and also buffers the water resulting in less pronounced pH swings.

Have you seen any signs of predators? Where do you live? How big was the missing koi? An arbor would deter many birds (but not always) so it may have been a raccoon or another mammal if you're in the USA.