I guess the relevant info would be:
The horse in question is a 4 year old gelding, Hackney/Hackney cross, about 14.2 to 15hh, and I'd put his body condition at about a mid-4 to a low-5. Since he is just 4 years old and hasn't been worked with much recently, he doesn't have the muscle tone to balance the right amount of fat. He has sort of a lanky teenager look.
His workload is minimal, just some basic groundwork from where he spent about 6 months as a lawn ornament before I got him.
I think the majority of our grass is fescue with a bit of bluegrass, but we've never seeded it for anything specific. It's what was growing naturally in the field when we bought the place. We put hay out too, but it's not any special type.
I give them sweet feed, but mostly as a treat since my understanding is that sweet feed is basically horse candy.
My knowledge on horse nutrition is pretty basic. I don't know anything about all of the assorted supplements that are available now, and I'm just now learning about the different types of hay. What I know about what horses eat comes from people who take a very simple, traditional approach - Horses eat grass (that's in the pasture), hay (that's in bales), and sugar cubes (that's when they're good) - if you know what I mean.
We're in a pretty rural area, but there's no shortage of feed stores, so I should be able to get what he needs easily enough.
As a related question, does it make any significant difference if we give the horses plain white salt blocks versus the brown ones with the added minerals?