With a CYA of 100, it'll take a few days for the chlorine to dissipate. If the CYA were lower, it wouldn't take quite so long. I would recommend a series of drain/refills to lower the CYA to around 40 or so, then stop using the trichlor tabs to keep it from getting that high again. Also keep in mind that the CYA test is a turbidity test, so cloudy water can make it test higher than it actually is. Might want to shock your pool and clear it up, THEN retest for CYA.
Also, your pH result is usually falsely high when chlorine levels are high, so the fact that it's that low after additions of Borax means it was probably VERY low when you started adding the Borax. How long did you wait after adding the Borax, and did you broadcast it or put it into your filter? If you put it in the filter, did you backwash, maybe backwashing it out before it had a chance to get to your pool? Using trichlor tabs will drive your pH way, way down if you don't keep an eye on it--that's why we recommend it only for vacations, establishing baseline pH and CYA levels, etc. and using bleach for routine chlorination and shocking.
Janet
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