On my first hot tub fill, I purchased a hose end filter from a local dealer, about 35.00. We have really hard and iron rich water, I used a combination of softened water directly and my unfiltered hard water hose with the filter. Got my tub filled, but the hose end filter was down to a small stream by the end.
This time around I tried a filter for RV water supply, about 10.00, for my drain and fill. I got two, put them on both the softened and straight water to double my filling. Once again, the unsoftened filter ended up greatly reduced by the end, but the water was great and I'm happy.
Just thought I'd share my little discovery.