Ok hun. So you were given bad advice from the pet store. You are going to want to do a total enclosure upgrade as mentioned already.
These are on sale for a great price on amazon.
https://www.amazon.com/Zoo-Med-ReptiBreeze-Screen-48-Inches/dp/B001PHABI8/ref=sr_1_1?crid=4KLRQTOX59E&keywords=extra+large+reptibreeze&qid=1555097484&s=gateway&sprefix=extra+large+reptibre,aps,200&sr=8-1
We can help you with humidity issues and how to combat low humidity. There are tricks for this while also maintaining the minimum size requirements and allowing for airflow.
I would really love for you to fill out this form in total detail. I would like to make sure you were not miss informed about anything else which is very very common.
Your lighting will need to be corrected as well. They got you to buy a compact bulb and he needs a T5HO fixture with a 10.0 bulb. You will want to get a 24 inch fixture to use on the new cage you need to get.
So I think your initial question of the spot is bug guts. Could also be dirt. He is at risk though for multiple issues should he stay with the current husbandry you were told to provide.
Chameleon Info:
- Your Chameleon - The species, sex, and age of your chameleon. How long has it been in your care?
- Handling - How often do you handle your chameleon?
- Feeding - What are you feeding your cham? What amount? What is the schedule? How are you gut-loading your feeders?
- Supplements - What brand and type of calcium and vitamin products are you dusting your feeders with and what is the schedule?
- Watering - What kind of watering technique do you use? How often and how long to you mist? Do you see your chameleon drinking?
- Fecal Description - Briefly note colors and consistency from recent droppings. Has this chameleon ever been tested for parasites?
- History - Any previous information about your cham that might be useful to others when trying to help you.
Cage Info:
- Cage Type - Describe your cage (Glass, Screen, Combo?) What are the dimensions?
- Lighting - What brand, model, and types of lighting are you using? What is your daily lighting schedule?
- Temperature - What temp range have you created (cage floor to basking spot)? Lowest overnight temp? How do you measure these temps?
- Humidity - What are your humidity levels? How are you creating and maintaining these levels? What do you use to measure humidity?
- Plants - Are you using live plants? If so, what kind?
- Placement - Where is your cage located? Is it near any fans, air vents, or high traffic areas? At what height is the top of the cage relative to your room floor?
- Location - Where are you geographically located?