Kingbud-
In an 18,500 gallon pool, every quart (which is 32 oz.) of 6% bleach will raise your cl by about 0.8. It will take about 1.5 gallons to raise your cl by 5pm. Most chlorine is sold in 3 quart jugs. Since 4 quarts is a gallon, that would be two 3 quart jugs to equal 1.5 gallons.

How high you need to keep your chlorine level depends on your cya level. Also, the best time to dose with bleach is in the evening. Test and then add however much you need to get back to the proper amount of chlorine (again, based on your cya reading). The easiest way to add it is to dump it in the skimmer while the pump is running and then be sure to run your pump for several hours afterward. Hope this helps.