Chlorine won't stay in pool

Help - I'm a new pool owner and would appreciate any advice, or a direct to info that's already been posted about this problem.

My inground pool is 16,000 gallons, I have a Nautilus FNS filter. When I bought the house in December, it had been empty for almost a year; the pool had a lot of debris in the bottom, mostly from the surrounding fir trees, but wasn't green or cloudy.

I hired a pool company to do bi-weekly visits, but the pool got cloudy last month. It turned out that there was a crack in the filter manifold; I got that fixed, and decided to do my own chemicals.

Went to the pool store and got DE, chlorine tablets, test kit (Ph, CC, alkalinity), algicide, shock, and granulated chlorine. Backwashed filter, added the DE, shocked the pool (company sold what they said would be enough to shock the pool), added algicide, vacuumed the pool - sorry, can't remember in what order. The result was that the chlorine and Ph levels were good.

The Ph levels have remained good, but the chlorine keeps disappearing. I've added granulated chlorine, used chlorine tablet in a floater, put in liquid chlorine, and shock, and the chlorine disappears in a matter of hours. The pool is clear. There's a layer of brownish residue at the bottom, but don't know if it's dirt. Underneath there's what seems to be staining, a light brown/green layer.

It's possible that I haven't shocked it sufficiently - is there an outer limit of chlorine I can/should add?

Hi and welcome to the forum. We really need a complete set of current water testing numbers to be able to offer you advice. Can you please post the following for us to take a look at:

We need at least 2 of the following:
FC (free chlorine)
CC (combined chlorine)
TC (total chlorine)

Also:
pH
alk
calcium hardness
CYA (cyanuric acid)

Is it a vinyl, gunite, concrete, fiberglass pool? Also, please tell us ingredient names of everything you have put in your pool --- not just "shock" but actual ingredients. Then somebody here can take a look at better advise you.

Chances are really good that your chlorine is disappearing because it's fighting something in the water and because your stabilizer is zero, allowing the sun to consume what the stuff in the water doesn't. Go ahead and post the info that Watermom requested, and I'm sure we can get you going in the right direction!

Janet