Tetra Pond GreenFree 9W UV Clarifier

Is there a gasket or o-ring that is damaged or bad? IF not you can run a bead of silicon around it where the surfaces join and let it dry before you put it together. This would make a gasket.

What size is your pond Length X Width X Depth. What temperature is your pond at? Is the pond located inside or outside? How big are the Koi? and how many are there?

A Uv-clarifier is simply placed after your filter on your return line.

A test tube brush or a small bottle brush will fit and not damage anything. Alternatively as long as it is not used for saltwater soak in a bucket of 5 gallons water and a 1/2 cup of bleach will kill and separate any algae. Just rinse thoroughly to flush out any leftovers and to clear the unit.

Basically flow is best towards the the socket of the bulb.

I have used a smaller version for years in the rain with no issues.

you should wait a week to make sure that everything is stable in pond and add your fish, avoid too many fish and overfeeding them. enjoy your fish pond, i love them.

Sure. But you may find it's less effective.

You don't need a bulkhead if your liner is EPDM. You can use a boot that is attached with adhesive that will seal you pvc piping. I don' t see a problem with dirty water going thru the pump before the filters. for some diagrams of settling tank installations see:
http://www.koipondfiltering.com/koi_pond_filters_diagrams_intermediate.html

For instructions and to get a new parts breakdown you call the Tetra Pond Division in Virginia toll-free 800-526-0650 any issues getting the right info, plan B is to ask for Product Manager Curt N.