Q.Arborvitae turning brown
I planted these 5-6 ft arborvitae that I got from Home Depot last August. I live in upstate NY and have been watering these consistently and keeping the soil moist so the roots would take. In the past month or so (sometime in April), 90% of these plants started turning brown from the bottom up. The only thing I could think may have caused it would be that I fed them Treetone. Do you have any advice on what to do? Are these guys goners or can they be resurrected?

I'm concerned you may be overwatering your Arborvitae. If the soil is constantly wet, the roots may become water logged and this will lead to root rot.
Though watering is important in the first few months after planting, you should begin to taper off on the watering schedule.
Also make sure the soil is draining. If you dig down about 8 inches and the soil is wet and soggy, you are likely watering too much.
I would also inspect the plants more closely for signs of pests or disease.
Boring insects can also girdle a tree and disrupt the trees ability to take up water. Look for small holes in the trunk and small piles of sawdust.
Application of spring fertilizers are generally not an issue, as the plants are actively growing.
I don't think the Treetone is part of the issue.
Here are some articles with more information.
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/winter-damage-to-arborvitae.htm
https://www.gardeningknowhow.com/ornamental/trees/arborvitae/fertilizing-arborvitae-trees.htm