So your suffering cloudy water syndrome at the moment, ok so nines out of ten it's indicating your pond isnt propperly cycled as of yet .
What test kits are you using please (1) test strips, (2) API drop kits, (3) Tetra drop kits if your answer to this question is (1) then get rid of it as test strips are not too accurate (2) or (3) are the best two kits on the market.
You say the pond has cycled when did you note the spike in ammonia and nitrite that indicate the pond is cycled?
Please could you tell me the results of your ammonia, nitrite, Nitrate, Ph Kh,Gh?
What size Aqua pond UV-C are you running, I ask this because we run the 36 watt one with the twin bulbs, where is it situated (1) before filter, (2) after filter ?
I'm a little confused as to which filter your running on the pond which of these is it on the link provided please :-
http://www.amazon.com/Aqua-Ultraviolet-AAV50073-Ultima-Aquarium/dp/B0002DJUNS
I ask this because from what I see most of these filters are rated less than your 3800 gallons US we only have a 1,000 imperial gallon pond for our koi but the filtration would run both yours and ours quite easily and still have capacity to spare ( our pond is a retro fitted purpose built koi Dealership QT pond capable of QT ing up to 100 6" koi for months at a time).
If you point point out which pump it is then we can look at its specs.
rgrds
Dave