could be spider mites. Look at the bottom of the leaves with a jewelers loop. They are very tiny.

The problem with growing Dendrobiums is that the species come from a wide variety of habitats, so your problem may be spider mites or it could be something to do with your growing conditions.
You should update your my page details to show your climate zone or the state where you live in the USA.

Hi arthurm, I actually live in the United Kingdom.

I noticed that the plant itself was potted in a small pot full of coconut husk, when researching it before it said the dendrobium likes stones and a rocky environment so I'm thinking of repoting it to a a mixture of coconut and hydroton.

It may just do the trick.

Do you live in the sub-tropical south or the cooler north? Lol.
This stones and rocky environment stuff relates to culture in the tropics (because a bark mix will quickly breakdown because of heat and humidity) or some particular species that are found in nature growing on rocks.
I haven't attempted to grow Den. bracteosum but the habitat indicates that it needs warm conditions all year, say a temperature range of 20 to 30C.
Have you ruled out red spider mite as the cause of the damage?

show a pic of the underside of the leaf...

I cannot be sure from the picture but what you are seeing could be caused by phyllosticta, which is a fungus common in dendrobiums. I have had it on mine in yhe past and just removed the infected leaves without too much trouble. But this year has been really rainy and mild so the leaf spotting has been a lot worse. So I just started treating mine with a systematic fungicide. It is too early to have results but I am hopeful.

Here is a link that might be useful: Phyllosticta fungus

I live in the Northern Hemisphere, Europe. Great Britain. East anglia.

Anyway, I tried several things, and I contacted the seller who was adamant all of his other dendrobiums are super healthy, which i don't really believe but I don't want to argue.

I sprayed the plant for three days in a row with insecticide and fungicide, also after that I sprayed it for another three days with a mixture of water and cinnamon. I spent a lot of time cleaning the leaves every day, with wet tissue and misting the plant in the evenings to increase the humidity as I have a southern window in my room and it can get really hot in the afternoons.
To be honest I have no idea what it was, but whatever was happening it stopped for now. It may be because I got annoyed and just sprinkled and covered the leaves with a layer of cinnamon and left for the night and then washed off.

That is the most stupid method of rescuing an orchid I know, but it seems to be fine now.

Hah... awkward.

I think you have eliminated the nasties. But next time spray once and wait a week to do it again as this will deal with surviving hatchlings. Make sure to spray underside of leaves especially if you think it might be mites. Good luck