Looks like a scratch or puncture. I would remove or rearange your decor. For right now I would bump up the heat and add salt. Have you used salt before? What is the temp currently at right now? Try to get it to 86' if it's not already. Also how big is your P bass?
just make sure your water parameters are good, and as mentioned earlier, use salt with water changes...no need for mela-fix...you really don't need to use that product...ever!