Evaluating gelding's nutritional needs

I feed my horse 2 oz whole flax seed daily. I did a bit of research before deciding to go with whole instead of ground, but grinding fresh at each feeding isn't an option where I board, so it was either whole or pay a lot more for a stabilized ground product. I don't see whole seeds coming out the other end, so I feel pretty good about it getting digested and used.

He is on the heavy side and always has been for majority of his life. A lot of it is his build in general. During his spring vaccinations the vet said he only needed to loose about 75lbs and we did manage to slim him down over the summer on 24/7 turnout and 1/8th cup ACV once daily. Unfortunatly he did put some weight back on for the winter, his ribs are still palpatable but not as easily as during the summer months but no excessive fat deoposits any where else, he is still on the ACV daily until this bottle is done (then again in the spring). It doesn't help he's not rideable right now due to the rain rot but as soon as its cleared up we'll be back to riding 3-4 times per week.

We did one medicated bath with a shampoo recommended on this forum but it's far too cold to continue doing that with the temp and winds here. We've been treating with vetericyn and MTG - going through both of those quickly because its everywhere. We've had worse wet seasons then this and he's never had a case before (stathe only change being 24/7 turnout) so I think a deficiency or stress played a roll at this. So I've been evaluating his diet and will be making changes over the next couple weeks and I brought him back inside since the last week he did seem overly stressed outside.

We'll be adding in the ionized salt, it won't be free choice. I am trying to think of ways to get that to happen when boarding. Plus starting whole flaxseed. My budget just doesn't allow me to buy a stabialized product at the moment.

I'd look into a decent Vitamin E supplement to go along with the Omega 3s in the flax. Vit E levels in hay decline rapidly, especially in hay that's been exposed or mistreated somehow as it sounds yours has, and low levels of Vitamin E are known exacerbate or make a horse more prone to skin issues (along with tying up).