Add as much air to your pond as you can using air pumps and air stones to distribute the air (highly recommended for ponds that are heavily stocked). You can add the air directly to the pond, the filter, the waterfall and anywhere else you can think of.
An all inclusive test kit, which enables the pond keeper to check on all the vital water quality parameters that affect the health of the pond. Includes test for Ammonia nitrite, Nitrate and Broad Range pH.