Not sure about the scratching...I'm assuming this is an acrylic tank rather than glass?...but I once had a Convict kept as a solo specimen who displayed an aggressiveness towards the front glass. I assumed he was attacking his reflection, so I fiddled with and adjusted and made several minor alterations to the light fixture above the tank. I ended up moving the fixture slightly closer to the front of the tank, but changing the angle so that it shone more towards the back. This completely stopped the aggressive glass-banging literally immediately.
As a happy coincidence, it also radically reduced the green algae growth on the front glass, as the amount of light actually striking the glass itself was lessened. This benefit is so nice that I always try to arrange my lighting this way just for that reason. Maybe coincidentally, I've never had a fish bashing his brains out against the front glass again.
Another thing to keep in mind is that reflections on the inside of the glass will be reduced if there is more light coming from outside the tank. They seem to be at their worst when the tank light is on while the room is dark. So try keeping the room light on as long as the tank illumination is on. An illuminated tank in a dark room makes for a dramatic effect, but it also is the most likely to have internal reflections.
If these ideas work, they work immediately; no reflection, no aggression. So if you try something and it doesn't work right away, try another slight change without wasting time waiting for results from the first try.
As a happy coincidence, it also radically reduced the green algae growth on the front glass, as the amount of light actually striking the glass itself was lessened. This benefit is so nice that I always try to arrange my lighting this way just for that reason. Maybe coincidentally, I've never had a fish bashing his brains out against the front glass again.
Another thing to keep in mind is that reflections on the inside of the glass will be reduced if there is more light coming from outside the tank. They seem to be at their worst when the tank light is on while the room is dark. So try keeping the room light on as long as the tank illumination is on. An illuminated tank in a dark room makes for a dramatic effect, but it also is the most likely to have internal reflections.
If these ideas work, they work immediately; no reflection, no aggression. So if you try something and it doesn't work right away, try another slight change without wasting time waiting for results from the first try.
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