How long does it take for the brownish-red to come out of the pool after you have shocked it?

That red stain is from iron in suspension in the water. You may be on well water or the city water has a high content of iron in it. The resulting stain possibly could be depositing if:

You are getting a chemical reaction from the minerals in the pool water and the newly added fresh water. You had just topped off the pool with fresh water and then added a fair amount of liquid chlorine right afterwards. With the above situation -- you can avoid repeated deposits somewhat by letting the fresh fill water blend with the old for several hours and with continued filtration

• then add the chlorine slowly and in small quantities. Or you

could test with the chlorine by adding no more than a quart of liq. chlor. and waiting to see if you get a reaction ~ a brownish cloud forming where you added the liq. chlor. If no cloud go ahead and add the rest of the gallon of chlor.

To avoid getting more stain on your pool you can add a sequestering agent which reduces the likely hood of more or heavy staining.

Unfortunately, the red stain will not come out of or off of the surface of the pool. That will take more drastic action such as draining the pool and having it acid washed or treating heavily with the iron remover sequestering agent but in most cases the later does not work well. You might try filtering the fill water as you add fresh. k