I am looking for some advice on moving my coldwater fish to a pond.

I currently have two fish in my Hagen Tropiquarium 68 which has a 72ltr capacity. I have one 6 year old comet, which is around 17cm in length and a 9 month old shubunkin which is 9cm in length. A family member has a pond that currently has 4/5 goldfish in it at the moment and I am looking to move my fish into the pond fairly soon. I have been advised, by many, that my comet should have progressed into a pond by now.

The pond is filtrated (by a recently renewed filter/pump) and has been in place for around 15 years, so it must be doing ok in terms of structure and habitability for comets, shubunkins etc.

What should my concerns be about moving the fish? Do I need to test the water levels as I have an API kit - although i'm not sure if this is needed for a pond. The pond hasn't been cleaned out since last summer as far as i'm aware, but as I say i've never kept a pond before so I don't know how often or how you clean out a pond that is home to coldwater fish. What sort of maintainence should be carried out on the pond?

I'm planning on converting to a tropical tank, which is the reason for moving my goldfish, however i'll save that for another thread in the appropriate sub-forum.