http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7405.html.

Part of the problem may be a drastic change in environment, but the white web could be spider mites. Mites are tiny and you need a good magnifying glass to see them. If they (barely moving) or their eggs are visible, move the plant way away from other houseplants and treat the problem. Thre are many sources for information and methods of treatment.

Here is a link that might be useful: University of California on line

Falling or shedding leaves are usually something cultural, rather than nutritional. In the end, we can usually trace the cause back to a decrease or stoppage of the flow of a particular growth regulator/hormone (auxin) across a special zone (abscission zone) that causes a separation of the leaf from the plant and its eventual fall. It often occurs from diminished light, especially quick changes from bright to less bright, too little water, or too much water. In short: decreased light reduces auxin flow. Auxin flow is required to keep an abscission layer from forming. No light - no auxin flow - abscission layer - leaf falls.

It also occurs from too little water. No water - no photosynthesis - no auxin flow - abscission layer - leaves fall.

In the case of too much water, the reason is a little more obscure. Too much water - roots rot or function/metabolism is compromised - not enough water to canopy - tree 'thinks' it is dying of thirst - no photosynthesis - no auxin flow - abscission layer - leaves fall.

If I had to guess, I would say it is a light issue - a change from bright nursery conditions to less abundant light in the home, but even something as simple as the upper leaves shading out the lower leaves, or possibly turning the tree so the side that faced the brightest light is no facing the room's interior. Sudden chill - as in cold drafts will also cause leaves to fall.

Look at the possible reasons above & the explanations, and you should be able to take an educated guess as to the cause. The question then turns to whether or not you can provide the cultural conditions to correct.

Never water on a schedule. Ficus won't tolerate wet feet well. Tip the container and water when the soil first feels completely dry at the drain hole. Soils feel dry to us when it still has about 40% moisture content. Plants can extract moisture to 30% or below, which gives us a 15% cushion after soils feel dry.

Get the mites under control ASAP. The misting you're doing is totally ineffective at raising humidity, and can even be counter-productive for a number of reasons, but it CAN help with mites. Mist with a 50/50 solution of 70% rubbing (isopropyl) alcohol and water, being careful to cover the bottom of the leaves & get the spray into leaf axils.

Repotting should be done in the month prior to the most robust growth (for F. benjamina), which would be mid-late Jun, for you. If you need help with the repot (which includes root-pruning - otherwise it's just a potting-up) stop back in the summer or head over to the container forum & do a search (tapla repot ficus) for specific instructions.

Good luck - take care.

Al