We have three large Ficus trees in pots that stay outdoors from May until September. Every year when they are brought back in they begin to drop their leaves. I am still picking up ten to twenty leaves a day off the ground. This will pretty much continue until they can go back outside, since I have no inside area where they get ideal amounts of light. I water all three plants once a week. They get between 1/2 gallon and 1 gallon each. One of my plants is very root-bound and will no longer take more than 1/2 gallon without overflowing the drainage tray. I'm planning on transplanting to a bigger pot soon (but it's a very messy procedure to do with large plants indoors). Your plant may be root-bound and need a bigger pot, or it may have an undersized root system for the size pot it's in. Either way it can't hold as much water as you're trying to give it. I don't think it would hurt to water twice a week, but I wouldn't water more often than that.
.......Jan

Watering is not a matter of how much at a time, but you must be sure that the entire root ball is saturated whenever you DO water. Oftentimes, soil will make channels that will allow the first sip of water to go right down to the bottom and out the drain hole. That means that large volumes of soil stay bone dry.

I prefer to sit my plants in a basin and water like heck. As the basin becomes filled with water, this allows the root/soil mass to become totally saturated. After an hour or so, I remove the plant from the sink or basin and set it back in place.

I strongly suspect that your ficus is not being watered properly, that it should be soaked upon watering. How many times per week depends upon how quickly the soil dries out. (I have plants that require once weekly watering, and others that go through this process once per month!)

Ficus will drop leaves every time it is moved from one light source to another and anytime it is stressed--like moving it from outdoors to indoors.

I let mine dry out fairly well before giving a few CUPS of water. Depends on what kind of soil you are using. Mine has lots of perlite and peat moss and vermiculite which makes the soil very light.

It also depends on the size of the ficus. If you have a tree of 5 feet you will certainly need more water than a tree of 3 feet. I think a gallon a week is really too much.

Nancy