OK,

I gather you probably shouldn't use any powdered chlorine in an SWG pool. "Shock" is a mis-labeling of powdered chlorine and it seems to have clogged your system. I'll bet it was Cal-Hypo as its dissolve rate is fairly slow.

I'm not the SWG expert but if your FC is down and you are seeing green, I'm guessing it's stopped working.

But I would start by adding 3 gallons of 6% bleach immediately and plan to do it two to three times a day just to clear your water.

DO NOT ADD ANYTHING LIKE CLARIFIER, FLOCCULENT, OR ALGAECIDE! And since you have a vinyl pool, don't add calcium either.

You'll need a good set of test numbers. Take a sample to the pool store but don't buy anything yet. Make sure they do your salt level as well.

Beware: they'll try to tell you your TDS (total dissolved solids) are too high, that you need PhosFree to reduce your phosphates and that you need calcium. DO NOT BE FOOLED. These things won't help you but will only make it worse.

I'm surprised you have no CYA. Your test may be fault or you accidentally back-washed it out--that happens as CYA takes a VERY long time to dissolve.

This is just for starters. As we know more we can help more. And the SWG folks will kick in with their detailed knowledge.