Artlyn2, I have a hot tub and pool and am on well with iron at 2 ppm.
For the hot tub in the winter I use well water as my outdoor soft water spigot is closed for the season.
On refill, I use a product called Metal Gon.
Amazon.com : Metal Gon/Defender Two pack : Leisure Time Spa Metal Gon : Patio, Lawn Garden
That will sequester the iron and turn you water clear. I also use a pre-filter, which gets 'some' of the iron out, but not all -- its called PreFresh filter and is good for about 8,000 gallons.
Amazon.com : Pre Fresh Garden Hose End Water Filter all purpose, pool, spa, hot tub, pets, car wash : Garden Hose Parts : Patio, Lawn Garden
For a heavier load, you can also use Defender, meant to be weekly maintenance sequestrant when you top up or to keep really high iron loads in check.
I don't use those spa products (Metal Gon and Defense) for my pool, only Metal Magic of Jack's magic...but those are way to strong for a spa and with high heat, its best to use spa products designed for same.
So that's the rx for immediately remedying your problem.
If you do have a whole house water softener set up or get one you can have it plumbed to include an outdoor spigot. But then if you use same in a spa, you will need to add calcium to control foam.
I wouldn't plumb soft water outside just for a spa...but I did for my pool, where metal was a big problem. For the spa, you drain and refill often enough that the Metal defender and prefresh filter are enough to do the trick without any unintended consequences