[Skimmerking]

you added all this within 1 month of starting up a new tank. with a tank that large its extremely hard to get your parameters to balance out. Even if you did get this sorted out it takes a long time for this body of water to level its self out. Having said that once you started adding all the fish the bio in the tnak is climbing and climbing the ammonia , nitrites and then to nitrates would build fast unless you are changing the water super fast. What about the sand bed new sand I don't see it taking 1 month to completely alive and working taking away the NO3. But with a tank are you not running a QT tank. you have a lot of nice stuff on there. but however have a UV light. its great and all but you need to source the ick from the start with a QT tank and then run UV light. nice tank BTW. but have the ick and the flat worms its a lot to deal with.
If you can get some flatworm EXIT I would use that.
as for the ick well lots of garlic if you cant take the fish that are infected out. if not I know a few people of tried draining the tank down to nothing hardly and taking the fish out that way Aquattro has done this and it worked .

that is a really nice tank and good luck my friend. I know what its like having a huge tank I myself had a240 gal 8 footer.