Question about Water Quality upon opening ?

Hi Everyone - I have some questions about pool opening and pool covers. I have an old loop-loc cover that probably is in need of replacement. Each spring, I spend about a week sanitizing the water in my 43k gallon pool. When I remove the cover, the water is black – it’s disgusting. It entails a lot of chlorine, DE, and cleaning the filter grids multiple times by hand. I've taken care of my parents pool for about 40 years. When I take off their regular cover with the pillows, I could probably jump right in. The water is close to perfect. I’m trying figure out why ? Is it the cover preventing stuff from entering the pool ? Their pool definitely receives more sun and has less leaf litter. I also need to be much more vigilant about combating algae as my pool gets afternoon shade and will get a mustard algae if neglected.

I'm not sure if disgusting water upon pool opening is normal ? I can say with certainty that the extra slamming that needs to be done will reduce the longevity of my liner. My parents lasted 23 years before I started patching it - replaced after like 26 years. So I’m curious what others think ? Is the condition of the water the result of having a mesh loop-loc cover ? or just the environmental conditions ? I was considering buying a large solid cover and putting it over the loop-loc next year, but not sure it would have any effect. Any thoughts would be appreciated. Thank you