When your pot are smaller, the plants roots will out grow the container, that will cause the root bound problem. Root bound will show stunted growth, stretching, smaller and slower bud production, easier to burn with nutrient solution, the plants need watering too often, and wilting. A root bound plant will always start yellowing with the bottom leaves and work its way up the plant until all the fan leaves are gone.
Solution: You need to transplant your plant into a bigger pot. The rule of thumb with soil is 1 gallon of soil for every foot of growth except for clones which can use a smaller size. So a 2’ tall plant will need 2 gallon container. First thing you need to do is gently remove your plant from the smaller container into a bigger container, Very carefully use your fingers to dig into the outside 1/2" of these circular roots, loosen them up and pull them gently outward. If the roots are extremely tight, you must very carefully slice a thin layer off the outside of the entire root-ball. Once you have tended to the roots It\"s time to replant it. Set the new un-bound root-ball into its new larger pot. Please be careful do not pack down this new soil, you want the soil to be settled but loose enough to allow the roots to easily penetrate it.