There are several reasons why a plant's leaves turn yellow--over watering is a big one, but so is under watering. But yellow leaves don't necessarily mean there's a fungal disease present. Let's start with basic money plant care. One yellow leaf isn't generally a cause for concern. 
Money tree plants like a mix of direct and bright, indirect sunlight and relatively high humidity. As with most houseplants, too much direct sun can scorch the leaves. To achieve the right balance with your money tree, turn or rotate it regularly for more even light distribution. Just make sure to not move it all over the place so as to not disturb it too much. Money trees can handle fluorescent lighting, so you're safe to keep one in your office as long as you take adequate care of it.

Money tree plants do best in warmer environments, so you'll want to keep them in an area that's between 65 and 75 degrees Fahrenheit. As far as humidity goes, money trees thrive with extra moisture, so it might be a good idea to mist your plant regularly or put it on a pebble tray to increase humidity in the winter.

Prune off any dead, damaged, or dying leaves/stems to keep the plant healthy. The best way to do this is to use clean, sharp scissors or pruning shears and make sure you wipe them off between cuts to avoid spreading any fungal disease that may be present. Judiciously pruning the leaves will  stimulate new growth if you cut in front of a leaf node.

Since money tree plants require a lot of water all at once, they can be prone to root rot. Root rot, if you're unfamiliar, is when there's too much water in your plant that causes the roots to decay and die. When you're watering your plant, make sure you don't see extra water sitting in the saucer under the drainage holes. If you do, clear it out to avoid root rot. Your best bet is to use a pot that isn't too big (the bigger the pot, the more room it has to hold water) and has excellent drainage. Place it on a saucer that you can easily remove, and dump out when it
fills with water.

Your use of Neem oil is a good idea to ward off insects such as aphids or mealybugs. But, your plant looks a bit tired. Perhaps re-potting it with fresh potting soil would perk it up. It's important that you maintain nutrient-rich potting soil with good drainage. To achieve this, you'll want to use a well-draining potting mix with perlite or add some sand and gravel for extra porousness.

How to repot:

If the roots are beginning to get crowded and growing through the drainage holes, it definitely needs to be repotted. Do this in the spring, using a 2" bigger pot to keep the roots drier. (As mentioned above, too big of a pot could cause the soil to dry slower, which is not helpful.) Water your plant in the old pot before transferring over and let sit an hour. Place a piece of screening at the bottom of the container over the drainage hole to secure the soil and allow to drain.

Add soil to the bottom to elevate the root ball. Lift the plant andrelease the roots against the existing planter. Use a clean knife or garden trowel to wedge between the pot and the soil to loosen. Inspect the root ball. Notice if there are any dead or rotting roots and trim off with sterile pruners. If the plant is rootbound, cut through the roots to alleviate continued encircling. Ensure the plant is sitting about 1" below the edge of the pot to avoid water spillage. Add more soil and backfill around the sides by tamping down. Fill up to the soil line but not over. Water thoroughly, leaving the soil damp but not soggy. If settling occurs, add more soil.

You should fertilize your money tree bimonthly during the growing period. Use a balanced liquid fertilizer at 1/2 strength. Reduce during the fall and winter months while the plant is in their dormant phase and refrain from watering as much so they can rest.

Take these steps and your plant will likely be healthier.