Stubborn, stubborn, stubborn organic stains

[RBEmerson]

Our Pebble-Tec in-ground pool has four major stains that refuse to die. Two are definitely related to winter leaves, while two are mainly "where things died" (worms, etc.). They're brown to yellow-ish. There's no metal within a few feet of the stains. Overall pool chemistry is in spec.

Ascorbic Acid? Laughed at it, and asked for more. I tried scrubbing with chlorine tablets. Waste of effort. Parked the remains of the tabs on the stains. Waste of effort. Dumped shock on the two shallower (4ft.) stains. Waste of effort (well, did shock the pool, as needed anyway).

I have the unhappy feeling the only fix is a strong session of oxalic and/or phosphoric acid, which means draining the pool (about 15K gal.).

Have I missed The Secret Cure They Won't Tell You About?

 

[1poolman1]

If chlorine didn't affect them, they may not be organic. Was the "shock" you used cal hypo or sodium dichlor? Cal hypo is stronger and, if they are organic, should work. I've never seen it not on a true organic stain.

 

[RBEmerson]

Forget the tabs. They're neither cal hypo or sodium dichlor. That explains why they had little effect. They're fine in a chlorinator, but not as a cleaning product.

The challenge, then, is how do I effectively place a load of cal hypo on the stains.

The shallower stains are just on the flat bottom, nothing remarkable able the location. The deeper two, however, are centered on the pressure relief plugs. Unfortunately, when the bottom was poured, the plugs went into a small depression. Dead worms, bugs, whatever dies over the winter, finds its way to the two depressed spots. Anyway, they're about 6' down. Again, the trick is placing shock where it can do the job on the stains.

Suggestions?

 

[1poolman1]

Forget the tabs. They're neither cal hypo or sodium dichlor. That explains why they had little effect. They're fine in a chlorinator, but not as a cleaning product.

The challenge, then, is how do I effectively place a load of cal hypo on the stains.

The shallower stains are just on the flat bottom, nothing remarkable able the location. The deeper two, however, are centered on the pressure relief plugs. Unfortunately, when the bottom was poured, the plugs went into a small depression. Dead worms, bugs, whatever dies over the winter, finds its way to the two depressed spots. Anyway, they're about 6' down. Again, the trick is placing shock where it can do the job on the stains.

Suggestions?

Most cal hypo dissolves slow enough to fall to the bottom of even an 8' pool. Just toss enough in the same area and it should get there. Stay up wind a even the dust will bleach your clothes. Not good to breathe, either.