How often does a bubbler system have to get cleaned? Also how often should the nutrients be added?

depending...you don't have to actually clean it till after the grow is finish...i would change the water/nutes every week to 10 days while in flower...you should know where you want your water level, so if it drop below there, top it up...that simple.
-sD

every 7-10 days period. veg and flower...good advice...most recommend topping off with ph'd rowater or whatever water you use, rather than using nute recipe, because of possible toxic levels/ppm's of one nute or another...hope this helps.lw