A 30 gallon is not a large enough tank for a sting ray, I attended a talk by one of the foremost experts on stingrays who said the smallest tanks stingrays should be housed in, is at least 300 gallons as adults.
Any light will grow algae if your nitrates are not diluted with water changes.
For most tanks with low light plants, I use shop lights from the local hardware store, sometimes 2 per tank way less than $50.