Periodontal disease - how often should I have hv scaling?

At your cleanings. Scaling is the professional removal of tartar buildup - it is done above the gum line. Root planing cleans the root surfaces made accessible by attachment and bone loss below the gum line. Scaling is performed at regular dental cleanings and good home care minimizes the tartar buildup. Scaling and root planing is a treatment for mild periodontitis.
Dentist's Judgement. The frequency of hv scaling in the control of periodontal disease is something that needs to be setermined by your dental professional. The type of periodontal disease you have, how fast plaque and calculas build-up, your pocket depths, micro-organisms involved and efficency of your home care all come into play. Remember that periodontal disease is managed or placed in remission, not truly cured.
Control the bacteria. Scaling and root planing leaves every type of bacteria under the gum tissue, just waiting for a chance to regrow. You have to be able to change the environment with something like the perio protect method that allows you to place medications into the infected area and begin to control the bacteria. Research shows 99.98% of the bacteria can be controlled with this method j dent res 2007.
Just once. I am not sure what is meant by "hv" scaling, but if you mean a deep cleaning or root planing, then you have completed phase i of periodontal therapy. Your condition should be reevaluated for the need of progressing to phase ii or a surgical approach. Repeated deep scalings is not the answer.
~3 months. I generally tell my adult patients who may have incipient to moderate (but controlled) periodontitis, that they should have this done every 3 months, trade off perhaps 2x year at gp's office and 2x year at periodontist's office. This is my generalized recommendation, so you must listen to the thoughts of your own doctor. Good luck!