About once a month I drain off about a third of the water. We don't really
measure it. Then slowly refill from the hose using a dechlorinator. We buy
the crystals and mix our own. Or you can degass the water by running it in
slowly over a trashcan lid exposing a thin layer of water to the air. That
is if you have something to set the lit on over the water. You can also add
water by letting it run down a waterfall. If you have chloromines in your
water that will not work.

Oh! Good idea about running it down the waterfall! I do have an
in-line dechlorinator I can put on my hose, but running the water
down the waterfall ought to give me an added measure of security.

When we do a draindown all the fish go in to an aerated child's kiddy pool
of 1/2 pond and 1/2 fresh water with a hardware cloth surround and net over
the top because fish jump. We also have too many predators here not to net
the top. I add plants and a floating cooler lid for them to hide under. They
go back in the next morning.

All right, thanks for all the good ideas. I've been nervous about
disturbing the fish too much, but I know it's a much bigger threat to
them if their water and pond aren't maintained properly.

Joan