pictures will definitely help. "jelly balls" or jelly like substance in a tank is commonly a fungal growth or a bacteria growth. when you say hairy what do you mean? green hairy? dark green/black hairy? white hairy? again pictures help alot. also more info in the tank will help.
tank size
filter
lights & light schedule
substrate
fertilizers
livestock
water parameters like:
ph
kh
gh
ammonia
nitrite
nitrate
TDS
also knowing maintance routine will give insight to what is going on.