Welcome to the wonderful world of pools and their care! As you see, there a lot of variables involved in getting to your desired stable state. I've found that removing/stabilizing as many of the variables as possible to be a good approach. So, use Pool Math calculator to determine how much CYA to add to get up to your target (70-80). You can buy either solid or liquid stabilizer. Liquid is generally a fair amount more expensive but much quicker. Solid does take at least a few days to fully dissolve. Some folks use the sock method, some disburse over the pool area, some pour slowly into skimmer. Try to test your chlorine level daily and be consistent in where and what time you draw your sample. Remember that even with that, you can have swings in "normal" chlorine level based on changes in bather load, sunlight, rain/storm...The final variables are pump run time and % SWG time. If you intend on leaving your pump "on" time constant at 9 hours a day, you can begin to adjust SWG "on" % using your consistent chlorine testing results. It's a process and takes a bit of time to "dial in" your SWG for your pool and it's normal usage. I don't try and hit a specific number, just a reasonable range (based on CYA level), say 3-6. I tend to go higher in the range just to ensure an unexpected pool party (they do seem to happen) or tropical deluge doesn't bottom out (or nearly so) the chlorine level. It sounds like you're doing OK and I wouldn't be too quick to lower the % until you 'stabilize" the other variables as much as possible. With pools, slow and steady wins the race....unless of course it's a green mess and getting worse! I run my pump on very low speed for 15 hours a day. In my similar sized pool this allows me to drop SWG % to about 30% to generally maintain about 5 ppm Chlorine with a CYA of 70. Under most conditions, this results in a slow "creep" up in Chlorine level, so occasionally I'll dial it back to 20% to let Chlorine drift back.
