I usually don't recommend adding more than a pint per 10000 gallons at a time, either diluted in a bucket of water ( i use one of the big 5 gallon buckets and fill it about 3/4 with pool water) and broadcast it over the surface of the water or walk it around the pool or poured slowly into the return if you don[t kilute it first. In a case where you have added a large quantity of borax (and it has dissolved) then it is probably ok to add about a quart per 10000 gallons. The idea is to add it slowly enough to give it time to mix so you do not have a pocket of low pH that can damage pool finishes or equipment. Brush down the pool walls after adding the acid (or any chems) and it will mix pretty quickly from the currents created by the brushing, usually by the time you have gone around the perimiter of the pool!