Regularly Check Your Pond’s Pumps & Pipes, Tubings, etc., Even the Seemingly-Functioning Ones.
You’ll never know when one of them needs oiling or a “rest” (you should have a backup or two at all times), or they will “blow” a gasket or a membrane, etc. Clogged or corroded pipings or tubings can also present problems, as well as those which have developed a crack. Also, check for some algae or organic-material buildup inside your pipings, tubings, etc. If there are some “dirt-collecting” components such as filters and/or baskets, check them too, and remove/clean what can be easily removed/cleaned every day. Exercising “eternal vigilance” for the general well-being of your pond(s) requires that “you leave no stone unturned”.