First off let me say big pool…small pool…same chemistry.
Sounds like you are using the 5 way test kit from WM. The OTO test in that kit measures total chlorine only so you should get a kit that measures free chlorine as well. I would recommend ordering one of Bens test kits. Another note is that WM kits don’t do well when testing other than chlorine when the chlorine is above 5 and if I remember correctly it mentions it on the direction card. There is an issue with the TH reagent on these kits witch is similar to the problem you describe. Test strips are not the most accurate. I would retest the chlorine using a dilution method with OTO. Take equal amounts of pool water and distilled water combine in one container and test with OTO multiplying by 2 for your result.
As for the pH…If it is truly that low you need to dose with some 20 Mule Team Borax to bring it back up.
Dont add any more stabilizer (CYA) or stabilized chlorine it will increse your CYA. I would use just bleach for your chlorene source.
Most of all read the forums and its sister site. You can dose using bleach calc. Get a good test kit. Put your pool info like size, filter, and general location in your siguture line. If asking chemistry question list your results. Listen to the pros here (I am still a noob) they know their stuff.
Steve