The first thing to do is to find out what the filter is doing and where it is in the cycling process. What are the ammonia and Nitrite readings for example? Are the ammonia reading stable or beggining to fall? A fall in ammonia is often followed by a rise in Nitrite but does at least indicate that the cycling process is well underway.
Next question. Have you tested your tap water? If it has choramine in it which means it has an ammonia content, you could be adding to your problems with your water changes as well as flushing away the very bacteria you are trying to cultivate!
How hard is your water? Hard water stifles the growth and reproduction of Nitrospira which coverts Ammonia to Nitrite. This means it will take a while for your Nexus to fully cycle. In my experience and based on feedback from other users, 16 weeks is not untypical to cycle in hard way areas.
Reduce feeding, add plenty of O2 to the pond to stimulate bacteria growth and try and avoid flushing away valuable water. Turn your UV off and think about adding salt to the pond if the Nitrite levels are above 1ppm.
If you can provide answers to questions I posed above, I may be able to give you a few more pointers.
Alan F.
Posted on Sep 10, 2006, 2:12 PM from IP address 213.120.101.21