I've inherited a mosquito-breeding pool, and need to close it.

[DewiMorgan]

From above list of chems in the shed:
"- TransChem "Muriatic Acid" 20deg Baume Hydrochloric Acid 31.45% - 2 x 1 gal" - unless you reckon it'll be horribly degraded by now, I'll try using those instead?

[PoolDoc]

Muriatic acid doesn't degrade with time . . . but bottles do. Be careful to set things up, so that if the bottle shatters, you are protected (glasses, gloves, running hose!)

If it's still in a box, move the box OUTSIDE before opening it. If you have a large enough plastic bucket, put one gallon in the bucket -- gently! -- and then poke it with a not-sharp stick, to see if the bottle is brittle. If the bottle is OK, proceed.

Be SURE to store the bottles so sunlight does NOT reach them.