Yes, we DO have a Fall season in Phoenix, albeit not very darn long. And there are some things you should and should not do to prepare your pond for the "winter" ahead.
Decaying leaves and foliage produce toxic gases that can harm your fish so you want to remove this debris before they can get saturated and sink to the bottom. If you have a skimmer on your pond, this helps tremendously. If you have any deciduous trees around, our Fall winds can blow them right into your pond. You don’t need to remove every single last leaf, but try to remove the majority. If you have a skimmer, check it weekly.
DO NOT Trim & Thin Your Plants Too Much
It's tempting to get everything "cleaned up" to prepare for winter. This is actually the worst thing you can do for your aquatic plants. We typically don't get any hard frosts in Phoenix; however, we can get a freeze or two. If you've trimmed and thin your aquatic plants too much, they will have no protection, and a frost could kill them. After the last danger of frost has passed (around the end of February), THEN you can go after any dead stuff and reveal the new lush growth getting ready to "spring" forward.
Aside from protecting the plant, if you have any amphibious life in your pond, they need the protection from the cold, too. They'll snuggle down into the heart of the plants and hibernate for the winter.
Use Cold Water-Formulated Bacteria
Add Cold Water Beneficial Bacteria to the pond once the temperature drops below 50 degrees, if you need to use any at all. You may not need it, especially if your pond is mature.
Stop Feeding Your Pond FIsh
Once temperatures drop to 50 degrees at night (remember, pond water more closely follows nighttime temps rather than daytime temps), stop feeding your fish. They need to get ready to hibernate and you’ll want to avoid any metabolic complications. You can feed them Cold Water Fish Food, or give them natural treats like melon, oranges, lettuce, and even Cheerios.
OTHER POSTS YOU MIGHT ENJOY:
TIPS FOR A HEALTHY LATE SUMMER POND
7 TIPS TO KEEP POND WATER CLEAN
POND WATER TREATMENT CHEAT SHEET