I have a gelding (15) who has arthritis with a noticeable bump. I have gotten his knee injected. He is a super "tough" horse, and doesn't show lameness but what supplements, etc do you recommend? I plan on Equivoxx when I run him but any other supplements that work good for arthritis specifically? 

I use MVP Exceed 6 way on my 2 older geldings and my younger mare with juvenile arthritis. It so far over the last 5 years has let me extend my injections out several months. I can usually get by once a year now instead of 6-8 months. You could possibly try the Buteless for comfort, it sure helps my 28 year old walk better when his feet hurt. You could also just do some MSM and then do glucosamine shots every other week. That's probably the most cost effective route. 

Also a liniment on it when you ride and run can help with some general inflammation. Or you cna use a PHT super bell on the knee or if BOT has something equivalent for a knee