After some deliberation, I decided to empty the pool and re-fill it, but I'm wondering, would it have been a viable solution to vacuum all of the algae and give the pool another shock, for good measure?
You didn't need to empty your pool. Plenty of people run into Algae attacks, it's not exactly the end of the world.
When you say you shocked your pool, you need to be way more specific on what you mean by that. There are guidelines out there that go into detail about how to shock a pool.
If so, it seems like a nice, simple solution to curing algae rather than all the testing, shocking and chemical balancing that I was trying initially....?
First off, shocking the pool can be done in 2 ways.
Using a powder shock mixture that may include Calcium or Cyanuric Acid including a High percentage of Hypochlorite (chlorine).
Bleach/Chlorine is the second method.
The reason why pool owners are required to maintain a specific level of chlorine is to fend off algae attacks. The fact that you turned off your pool pump had nothing to do with why you got attacked, but because your chlorine levels are probably 0 ppm (parts per million).
Now, I would agree with you that shocking a pool, and constantly testing is costly and annoying. But depending on where you live, emptying your pool can be even more costly. If your pool is 30,000+ gallons. Get ready for your water bill to triple that month. Shocking your pool might only cost a fraction of that price.
I was just trying to ascertain whether vacuuming the algae from the bottom/sides would have left the water as clean as it appeared to be...?
No, Even with your filter at 100% Clean and functioning. Algae is cleaned with a killing agent (Chlorine). Not your filter. The filter is mainly used for collecting dirt (AKA DEAD ALGAE).
Lets say you swept the sides of the pool and vacuumed the remaining algae.
First, the odds of you cleaning every inch of your pool is unrealistic. There are going to be nooks and crannies where algae will remain and then begin to grow all over again.
Second, lets say 99.9% of all the green algae got stuck in your filter. Your filter isn't going to kill the algae, it's just going to sit in your filter. And eventually break away from your filter and move back into the pool. You have to kill the algae. The dead algae then gets collected back into your filter and stays dead.
Don't you think if filters could simply catch all algae and kill it, the chlorine industry would have dead off long ago? People would install 2 or 3 filters and avoid ever paying and arm and a leg for chlorine on a yearly basis.