Open Green and Cloudy & No CYA

[Watermom]

You don't want to actually measure muriatic acid as it is too likely to splash on you. Just estimate your dose. I'd probably do about a quart and then after awhile, retest and redose if needed. Please read the info at the following link about using it safely.
http://pool9.net/ma/

[PoolDoc]

Since we don't know your TA, add approximately a pint - 1/8 of a gallon jug. Don't measure, just guesstimate.

Wait a day, and retest.