Eleanor Kellon, VMD
First, the easy stuff. No, WSC does not matter. You don't have to soak this hay. Also can't rely on those pellets to always be safe. You are better off with more rinsed-soaked-rinsed beet pulp.
If not soaked, your current hay has adequate calories in 20 lbs but does need mineral balancing (badly!) and supplementation. About 1 and 3/4 scoop of Uckele U Balance Foundation is a good fit until you can get a custom or add individual minerals. Stop everything else except plain white salt. Give vitamin E. The protein is just adequate in total amount but lysine deficient. The U Balance will help with that but would also add a dose of their Tri-Amino (inexpensive).
Poor chewing though will reduce what he can extract from the hay. It could be loose teeth, gum disease, poor chewing from age related changes in jaw angle or any combination of those. Contact both Ontario Dehy and Triple Crown about availability of the timothy balance cubes. If you have some large, heavy shears can also try chopping up his hay for him.
ACTH is still way too high and will also lead to weight/muscle loss. Talk to your vet about increasing this. Also consider putting him on Jiaogulan both for feet and to protect against pergolide veil. Some horses need APF for the veil but others do well with just Jiaogulan which is much less expensive. If you order the Uckele products, can get your Jiaogulan there too.
EC Owner 2001