I keep running out of iso

Mixalis

I'm cavalier and I get a good amount of 5* every week + and to rank 5 those 5* and rank 2* six stars take a ton of iso. I get iso from opening crystals and it's still not enough. I can't do arena because of work. I've completed everything up to act 6.2.2. should there be more ways of getting more iso 8? With rank 3 6* in the verizon, I'm finding it harder to get iso 8. This isn't 2015, when iso was enough for 4 stars.