the only secret to using shock is you need a digi scale accurate to 0.01 grams.
0.10 grams of HTH pool shock per 10 gallons of water is 1ppm free chlorine.
up to 5 ppm is safe for plants and humans
if you have rot, i'd run around 3 to 5ppm to get rid of it once or 2x a week. then for maintnenance, use 1 to 2 ppm once or 2x a week.
i don't like peroxide personally but many people use it successfully.
if you want to run beneficial bacteria ( i do now just to see how it works), pick up a bottle of Southern Ag Garden Friendly Fungicide. same bacteria as Hydroguard but a million times more concentrated. and much cheaper.