Of course your local pond storm will recommend completely cleaning out your pond once a year.
It creates the most amount of work, demands the most amount of purchases from the same local pond store,
creates more problems that will need to be corrected by products sold by your 'dearest' local pond store, and on and on...
It's crystal clear: By telling you to drain your pond once a year, they're creating more business.
A pond should NEVER need to be emptied and cleaned out. (not unless you're planning to add to it)
Just like when your house gets dirty, you need to pick up the big dirt, and vacuum up the rest.
(By the way, this is another GREAT reason for a bottom drain. All you'd have to do is net out the leaves and then turn on the bottom drain for a few moments)
By the way, when you empty and clean your pond, you will removed 99.99% of the good 'beneficial' bacteria.
So after filling the pond and starting the pump, you will have to wait for about a month for the beneficial bacteria
and the natural equilibirum of the bacterial processes in your pond to get back to normal and 'healthy'.
During this time, your fish will be stressed, and may get sick. Huge algae blooms will most likely occur.
Then most newbies start tinkering, adding chemicals, effing up the balancing process that was already effed up by draining and cleaning.
So the pond takes even longer to become balanced. For some people it will NEVER balance because they will not stop effing with their pond.
Mother Nature takes care of her own...and if you'd just allow her to help and do HER job, she'd take most of the work out of your hands.
Right now, all you need to do is a half day of vaccuming, and netting out leaves.
Not days and days of the work needed to empty and drain a pond, move the fish and plants, then clean it, then fill it,
then watch all hell break loose while it tries to balance itself again.
(and then we all get to say we told you so...
)
So I totally agree with what Cath said.
By the way, Microbelift is not a chemical. It's all the benefical bacteria that the pond needs to balance itself.
That's how it works. Basically: Mother Nature in a bottle.
http://www.microbeliftstore.com/home/ml1/page_5_7/microbelift_pl_16oz.html