It sounds correct, do a 25% water change between treatments. Do a gravel vacuming with the water changes. A bare bottom tank would be better if it's possibile for you to do. Add the excess to whichever tank you feed last doesn't mater.
Maybe it's caused by camallanus worms. Has he had any other new fish with him in the last few months? Have you bought new fish within the last few months?
http://www.fishlore.com/fishforum/f...23-how-get-rid-camallanus-nematode-worms.html
http://www.inkmkr.com/Fish/CamallanusTreatment/CamallanusTreatment.pdf
http://www.inkmkr.com/Fish/CamallanusTreatment/index.html
Where to buy:
http://www.foyspigeonsupplies.com/medications/worms-wormers/586-levamisole-powder (in PA)
http://www.nationalfishpharm.com/products3.html
http://www.inkmkr.com/Fish/ItemsForSale.html
Ebay