Well guys ive used a hefty uv steraliser on my 5000 ukg pond for 6 years (dont forget to change the bulbs regularly!) and it kills all the bacteria in the water, else why would you have filters?!!!! the filter house the nitrifying bacteria (obviously) and that is where they stay was well as on gravel/tank sides etc so everyone should use one of these beautys' my pond fish have never suffered from any illness practically ever! and there daddy size 
Edit- it also is inline to the tank's intakes (home made 100gallon filter) so my filter wont house any bad bacteria either - in a word SAFE!
Edit- it also is inline to the tank's intakes (home made 100gallon filter) so my filter wont house any bad bacteria either - in a word SAFE!
