"Hal" wrote in message
When I had a mix of goldfish and koi, it was not unusual for me to
find a small goldfish that had gone down the bottom drain to the
filter barrels and was growing faster than the ones living in the
pond. I started netting them out, but could swear some of the same
fish were back the next time I cleaned the filters.

Ditto, course I think mine were sneaking into the prefilter as that is
where most of the tadpoles ended up after I started the filter last spring.
I could always tell when a fish was in the prefilter as I couldn't find a
tad pole (they went into hiding amongst the screening on the bottom). Once
the fish was taken out the taddies would come out.

The lily pond prefilter has a different set up then my koi pond one where
it is up flow thru layers of screening. DS made a cylinder of screening,
with the pipe to the pump chamber going into the center. Thankfully there
were folds at the bottom for the taddies to save themselves. He has since
removed that for a neater appearance once the taddies grew up and next year
there won't be any taddies as the fish will be in the pond during their
mating time. (I'm hoping they'll go to the alternative quarters I'll have
for them.)

Anyway.... at one time I found almost all my goldfish in the pre-filter as
if the one had told the others of the big feast down the pipe. Thankfully
after a scolding, and probably growing bigger on tadpole snacks, most
stayed out of it after that.

All comes down to design both of the filter and bottom drain style. In my
koi pond they wouldn't fair as well stuck under the screening till I
cleaned it and there is more turns in that pipe and faster flow, but the
koi are too big to get in. The lily pond set up is perfect for a ride and
fairly easy for me to net them out as soon as I discover them gone. Next
year though I expect most of the adults to be too large to fit between lid
& liner and with the anti-vortex lid, the pull isn't that strong in any
given area. Not looking forward to netting out a lot of fry.... who may
find themselves living in the prefilter for a bit growing. ;-) ~ jan
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Zone 7a, SE Washington State
Ponds: www.jjspond.us