Chlorine of 13 is not high enough to shock the pool with CYA so high. That is why I suggested you add 4 jugs of bleach last night. You added 2 which only took you up to half as high as you needed it to be.

It may be that you lucked out this time with the chlorine dropping so low (0.5) and nothing is brewing but it is just safer to assume there might be an impending bloom and go ahead and shock to high enough to kill anything that might be getting started. So, test it again this evening and add however much bleach you need to take it on up to 25. An hour or two later, test again and note the reading so you'll have something to compare it to tomorrow morning when you test. (Need to be within an hour of sunrise. Otherwise you can't tell you much chlorine loss is from fighting something in the water and how much is just being lost to the sun.) Like I said, OTO is not super accurate but all you have to use at this point so just make a judgement based on the color chart that I linked for you above.

If you don't lose more than about 1ppm overnight, you can let the chlorine drift down. Always keep your chlorine between the minimum and maximum on the CYA/Chlorine chart and you'll avoid problems.

It is fine to vacuum to waste to try and lower the CYA but just be aware, your CYA may not be 100. It may be 200 or 400 or ?? Who knows. So, it may take a lot of water replacement to lower it. You might just want to try and live with it. It is ok to have a high CYA pool as long as you run the chlorine at levels that will compensate for it. We call this a HiC2 pool. (High CYA and high chlorine.)

One advantage of having a high CYA pool, is that in most cases it allows you to go longer between needing to add doses of bleach. Some people can get by with only adding it once or twice per week and still stay within the needed chlorine range.

A disadvantage is that if you do have algae, it will take lots of bleach to clear it since your shock level will be so high. But, you can avoid that as long as you never let the chlorine drop below your 'range.'

Just something to think about. Hope this helps. Let us know if you have further questions and keep us posted how things are going. (And order the K1515 ASAP. You need it!)