this horse use to get soaked alfalfa cubes twice daily but I'm concerned that's too much sugar for him now....what else can I soak like that, that will absorb water??...I thought about beet pulp but it's made from sugar beets...didn't know what the sugar content of that would be.

I have a recovered laminitic and I used to stress over every little thing. Alfalfa is actually very low in sugar and starch so is considered safe for laminitics. Hallway feeds makes a feed called Fibrenergy. Only has a 10% NSC ( Safe for laminitics) and makes a great mash to get more water into them. 

Check out Timothy Hay Pellets and other Hay Pellets that are soaked and compare their sugar content to each other. 

You can get beet pulp with out molasses. No sugar. Add2 tablespoons white salt to soaked feed and a probiotic.