Tank is minimally filtered with a sponge filter using an electric pump rather than air. A few weeks ago I thought I had conquered cyano in the tank but since the water sprite has increased dramatically it has returned - but only on the water sprite. At the next lowest setting the plants are all driven to the far end (from the pump) of the tank and stay static. I have now decreased the light intensity and will stop liquid ferts until the water sprite starts showing signs of distress. (I increased both when I thought the problem was resolved). The flow is directed across the back wall and on the surface - so its not the maelstrom the video suggests and the gouramis and otos are all in their usual areas.