No, dechlorinator removes the chlorine and heavy metals from tap water. A filter grows beneficial bacteria which breaks down ammonia into nitrites in nitrates, thus keeping your water quality good, you need to dechlorinate your water though for this process to happen. When you start up a new filter, it has none of this good bacteria, so you need to cycle the tank i.e. carefully establish the benefecial bacteria in the filter etc.
The filters purpose is to suck waste from the tank into the filter where the bacteria lives, where the waste breaks down as the bacteria absorbs the ammonia from the decomposing matter. The filter also provides surfaces for the beneficial bacteria to live on, and a constant supply of oxygen via flowing water.
By the way, nice looking pond

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