My pool gets a lot of organic material from the yard. A lot of tiny bugs (ants, spiders, potato bugs/sow bugs, earwigs and another harmless insect I haven't figured out yet) fall into the pool often. The chlorine level has been kept high greater than the minimum level at all times. (CYA 60, and FC >= 5). Pool brushed once or twice a week manually.
I got a backswimmer in the pool about two months ago. I fished it out and killed it. I saw really really tiny water beetles (just 1/2 mm or 1/4 mm) in the pool about 6 weeks ago. Perhaps 2 or 3 every day for about 3 days. Couldn't catch them because they were tiny. But they weren't there after a couple of days. I saw a waterboatman on the wall about a month ago. Fished it out and killed it. You can see those bugs very clearly on white plaster walls. The water beetles were the one that concerned me the most because they might have been hatching in the pool. The waterboatman and the backswimmer must have flown in as they seemed to be adults. They haven't returned.
About a year ago, I had a couple of hundred of these bugs, mostly waterboatman, a few dozen adult water beetles and about a dozen backswimmers. There were just a few to start with, and after a day of trying to figure out what those bugs were, there were many more and increased to hundreds. I shocked the pool, brushed the wall twice a day and it took about a week for all those bugs to disappear. Whenever I saw a backswimmer, I fished it out and killed it. The waterboatman and the beetles were the first ones to leave. A few backswimmers were hanging around either waiting to be caught and killed and finally those bugs left the pool too. They certainly didn't seem to mind a shocked pool. I didn't have the testkits then and so never really kept track of the chemical levels.
I think that regular brushing of the pool walls and the floor is essential in addition to keeping a minimum level of FC.