From what you said, it sounds like your CH level might be 125, but you didn't explain what you did clearly enough for me to be sure. CH certainly isn't 20. It is very common for the CH test to take more than 10 drops of R-0012, twenty, thirty, even forty drops are all fairly common. You should do that test again and be patient and see how many drops it really takes to turn blue.
Before fighting algae, it is best to lower your PH to around 7.4. You don't need to hit a PH of 7.4 exactly, anything from 7.2 to 7.6 will be fine.
Getting a CYA reading is important. If all you are missing is the mixing bottle, it is fairly easy to rig up something else. You just need equal quantities of pool water and reagent and a way to pour it into the view tube fairly slowly. If you have a dropper bottle that is empty you can figure out what half full is and mark it and then use that, or rig something else up.
Chlorine and D.E. have nothing to do with each other. I get why you are asking about chlorine, but I don't understand the reference to D.E. Perhaps you could explain that.
A SWG is not suitable for shocking. When shocking you need to add chlorine very quickly to get up to shock level. A SWG is designed to add chlorine slowly, which isn't what you want. You can use the SWG to supplement the chlorine you add manually. Bleach is usually the simplest way to add chlorine quickly. Be sure to get a CYA reading first, so you can calculate the amount of chlorine to add.