With 4500 gallons, 1.5 gallons of 6% bleach will raise the chlorine by 20 ppm. 1 gallon brings it up by 13 ppm, so the one gallon that was added two days ago was starting on the right track. The thing is the chlorine gets used up PDQ killing off the algae, so you need to read the chlorine levels 2-3 times a day and as much as required to keep the level up.

If you add 1 gallon in the morning to a black/green pool, it will be zero by night. You need to keep the chlorine level high, or else the algae will grow back. It sounds like your hubby added a gallon, it probably lightened up, but then the chlorine was gone and the algae came back.

If the CYA is low, try keeping it at a minimum of 15 ppm and the green will fade to cloudy, then finally clear. There should be a lot of dead crud in the bottom of the pool soon enough, vacumm it to waste. There are a number of recent threads on this topic so I'd recommend looking around. But before that, go hammer the algae with lots of chlorine to start.