Fin rot and losing scales - goldfish

Question
Hello-
I have a five year old goldfish - 15 gallon tank with a bio filter.  He lost some scales last week and lost a few more a few days later (maybe 15 total) - Prior to that he was somewhat lethargic but that seems to have passed.  He has also had white flat circular spots on parts of his tail which I understand was ick and have treated with coppersafe, though not as consistently as I should have.  He has had issues with constipation before which I have succesfully treated with peas.  Last night he lost the bottom portion of his bottom tail fin - maybe 1/8" wide and as long as his tail.  He still has most of the bottom fin intact.  He is swimming well and eating.  Today I put in a dose of coppersafe and a dose of melafix as per recommendation from a local fish store and plan to continue the melafix as recommended for 7 days.

The only thing that's recently changed for him is the addition of a plecco - he had constipation prior to the plecco, but never skin issues.  I have had the water tested and it is fine.  He eats  soft sinking spirulina pellets everyday.  

Any thoughts would be greatly appreciated.  Is it the plecco that's causing the problems?  Am I correct in thinking this may be a combination of fin rot and ick?  Please help!  :-)  Thank you.

Answer
Hi Lynn,
Thank you for your letter. It could be the plecto attacking him, especially since he's getting older and more sedentary. If you see any aggressive behavior from the plecto, then you will have to separate them. It could be the plecto, especially if he is large (more than about five inches). Fins may grow back over a long period.
Overall, though, it sounds like a water pollution problem. In my holistic system, I do not recommend the use of chemical treatments. See:
http://steamboats.com/aquarium.html
Please print this page out and consider switching to holistic aquarium care. It depends on prevention (stop over feeding) and creating a natural enviornment (using the product "Cycle" for friendly bacteria).
Your goldfish can survive on less than one spirulina tablet a day. Spirulina tablets come in different sizes, but figure one fish flake per square inch of fish per day, and then compare a fish flake to the spirulina tablet.
If your water is cloudy or viscous, follow the "emergency care" procedure at the bottom of my web page.
If you want to discuss further, please write back.
Nori