When you vacuum to waste, you are also vacuuming out your salt. Forget salt levels while doing so and while the SWG is off. Add salt once you get ready to re-start the SWG.
Now, with that said I think we should start with some basics. Start with pool school (white button atop right this page) and read it all more than once, if not ten times.
The dirt that is in your pool has organic matter in it. It is not sterile and has likely consumed more chlorine than the SWG can produce. Chlorine is consumed by organics and sunlight, so first we need to know what your chlorine level is plus combine chlorine. What do you test with? A FAS-DPD test is what you'll need, and your most valuable tool for your pool.
If you don't have a test kit, you can take your pool water to a pool store for a free test. The results are not reported to be accurate but it will work to get you started. Do NOT buy anything they recommend. Smile and say you already have whatever they try to sell you. Your pool needs none of those expensive products.
Go to walmart and buy plain unscented 6% bleach. In the laundry aisle. Get about 6 jugs for now. You are going to chlorinate with liquid chlorine for a while because the SWG can't handle what needs to be done to your pool, so it gets to nap.
I have a feeling you're going to need to shock the pool, but test results will help determine that. Do you know your CYA level? Knowing this is essential to figuring out how much chlorine your pool will need for the next few days till you turn the SWG back on.
You've got a couple things going on right now that are messing with normal operations. Solids (dirt), and little or no chlorine. Yes, get the solids/organics out but you have got to chlorinate in the meantime. The solids will either fall to the bottom or be swept into your filter and caught eventually. Sand filters take longer to clear particulates, adding DE to the filter sometimes is recommended. 1 cup, replaced after backwashing. The solids will fall all on their own, don't add anything to the pool other than chlorine right now. Do not buy that product, there's little to no chance that you need it.
Next, even if you don't need to shock the pool (you very most certainly likely do...) with the SWG off you must chlorinate manually. Use bleach, and the pool calculator
http://poolcalculator.com.
Onto shocking. Pretty sure you're going to need to do this so plan on it. Maybe get 10 bottles of bleach instead of 6.
Read the shocking information in pool school. Follow it, disregard the SWG till you're pool is done with the process, clear and ready.
Then add salt to the level needed, let it dissolve and start up the SWG. When you're done it will chlorinate just fine, you just have too much for it to handle right now plus we don't know how it was started up either. Proper SWG startup requires a day minimum of manual chlorination, this may or may not have been done.
Did I mention getting your own test kit? :~}