OK. Here is my writeup for bottom feeding wells where you are using liquid bleach for sanitizing.
https://terrylove.com/forums/index....izing-extra-attention-to-4-inch-casing.65845/
I expect maybe 2 years between sanitizings, but conditions can vary.
You might find something in there that you could adapt to your sanitizing if the method that you used does not seem to have done the job. The key points are to reduce the pH to about 5 or 5.5, get the chlorine strong enough for long enough, and drain the bulk of the chlorinated water to somewhere other than the septic tank. You don't want to put it on the lawn either. Maybe you can route the water to the gutter or ditch. If your chlorination killed off the problem stuff, then good deal.