Fredrick - The Nitrite levels are not raising as fast now. The last water change was probably over a week ago and today the level was .25mg/l.
There is nothing rotting in there. It's an ornamental pond with no plants. Just water, a pump and air stones.
I have notice though that the Titan 2000 pump collects solids underneath rather then send them all to the filter so I have got in the habit of sticking my pondovac under the pump weekly to get rid of any waste that is hanging around.
Otter - The strips were new. The problem is the scale. They don't read the low levels we wish to test. There needs to be 10mg/l before they start to show any colour change.