I would say keep up with the water changes and make sure you keep the proper dose of salt wich would be 1 tablespoon of salt per 5gal also raise temp to 86-87 degrees and increase areation. For more help i would really recommend you visit OSCARFISH.COM its a great forum for oscars. A word of warning is that everyone there will tell you that your overstocked by having and oscar bp pleco and the other fish in the 75gal. Good luck.