Zkittles

Depends on how old is the plant, if you have a young plant you need most of the container filled with water to let the bubbles sparkling hit the root ball but, older plants with big roots can reach the bottom of the container so you dont need to fill it to the top because roots already touch the water. You can fill half or less of the container.

Topping, defoliating and reduce your light intensity. Not too many ways I can think of off the top of my head to slow down her growth in hydro. Soil you can keep in smaller container to slow em down. Reducing feeding will slow her down but will probably cause deficiencies and reduce overall plant health.