When is the last time you cleaned it? Also do you have gravel or sand for substrate? Thirdly do you have any hollow decor? Like fake sumps or logs in your tank?
cleaned the filter this last weekend, no decor except rocks, and a medium sized bubble thing. that is why I am scratching my head. nothing in there basically except my fishie. 6 years old and never any problems! I am stumped!!!! a very little bit of algae on the back of the tank. gonna clean that today. like I said though, very little. gravel on mixed with a little bit of river rock. been in there over 4 years.
I just added a cap and a half of the prime. And going for a bike ride, then will try testing it when I get back in about 3-4 hours. Thank you so much for taking the time to help me out. I will post my test results when we get back. I sooooooo hope this helps. If not, I guess I will try changing everything out in the filter, but didn't think I had to do anything but clean if off.
My advice is get another tank or container for the purpose of a hospital or temp home for the big guy. Do 100% water change in the 75 gal, clean the filter(add some bac cul when done), clean the gravel .... as if it's a brand new setup. Let it cycle for a few day. Test water make sure everything is a go and then transfer the fish back to the 75 gal. Less headache and the problem is easily solved. Constant water changes and medication and chemical treatments is going to stress the fish out even more just do a transfer.
I guess I will try changing everything out in the filter, but didn't think I had to do anything but clean if off.
I disagree with this. Not that it's wrong, just unnecessary imo. If it was ammonia I could justify this but for nitrates big wc's should work just fine