Hi,
Well, yes that counts as carbon enrichment. In fact it might easily count as not enough carbon enrichment depending on a few different factors, so I recommend that you get into the habit of replacing at least 140L of water every week, and more than that if you can.
If you keep the lighting low, you can reduce the nutrient loading, which will reduce the growth rates and reduce organic pollution. Then you can get away with changing less water if it bothers you.
Cheers,