Salt systems are over-sold.

By this, I don't mean they are bad things -- I have salt chlorination on my remaining local customer pools. But I mean
+ They do NOT auto-magically solve all your pool chemical problems.
+ You STILL need to test your water.
+ And when something goes wrong, you STILL have to do what it takes to maintain your water chemistry.

Salt water chlorine generators (SWCG) are just that: simply a way to make chlorine and add it to your pool. They do the same thing a Trichor feeder does, or a peristaltic pump feeding bleach. If your SWCG is sized well, it will make enough chlorine to treat your pool during normal conditions, but it will NOT make enough to clean up your pool when you are having problems!

In your case, do this:
#1 - add 6 gallons of *plain* 6% house hold bleach to your pool this evening. (~ 12 ppm chlorine, on your pool)
#2 - check your chlorine in the AM with an OTO (yellow drops) kit. You should be dark yellow. If not, repeat the dose.
#3 - check again in the late PM. Again, if not dark yellow, repeat the dose.
#4 - get your CYA tested if possible -- the correct algae killing chlorine dose for your pool depends on your CYA level.
#5 - order a Taylor FAS-DPD testkit (Amazon link below in my sig) so you don't get in this situation again.