At 80 degree water temp. you have a saturation index of +0.3. That's not so bad. You could try to reduce your TA to like 80. There's a sticky on how to lower your TA (basically lower Ph way down and then aerate). Although you should give priority to the levels required by your SWCG system I think. Your Ph is also a tad higher than it could be. My point being a positive saturation index indicates that you are more likely to get scale. So what you may be seeing is suspended preciptation.

I'd bet that your sand filter needs attention. It doesn't seem to be getting the particles, cause your chemistry is just not that bad. Do the DE test. Pour a cup of DE powder into your skimmer. Watch a return and if you see a cloud of DE returning, your filter needs attention. I have read about many with sand filters who use DE on a regular basis because it provides filtering for amaller particles. After backwash, they replace it. If the pool is 8 years old and the liner seems to need attention, I'd bet that the same attention was paid to every other system in the pool.

With regard to salt testing, Doc has a sticky for finding the best test kit in "Testing and Adjusting Pool Water Chemistry". He recommends AquaChek salt strips for salt, or the Taylor k-1766. Both can be tricky to use. Strips require immersion for at least 5 and probably 10 minutes.The drop based kit is more accurate.

Read more, there's lots to learn.