How often to demagnetize mc cartridges?

Just bought a used sumiko fluxbuster and demagnetized my Lyra Etna for the first time.  Pretty nice improvements in sound!  How often should cartridges be demagnetized?
I try to demag every 50 hours of play. The Cardas album deflux treatment is also one of my protocols. Enjoy the music
Depends on how the coils are constructed. If iron core, the core can be magnetized. Then an occasional hit with flux buster is worth doing. But not very often.
@lewm , would you say that I need to rethink my protocol as stated above? My cartridges I am using in rotation are the DRTxv1s, ZYX original copper Universe, Shelter 901, Koetsu RSP, AT ART9 and ART7 and a Grace F9 SS optimum line contact, the latter MM I do not demag. I have followed this protocol with no derogatory results, that I can tell, but wonder if what I don't know might be hurting me in this matter. Looking forward to your response, not trying to bait you on this, do believe that it is pertinent to the OP. Thanks
I don't know how the cartridges on your extensive list are made.  Except for the ART7, which I do know has an amorphous core coil. I think that one contains no iron, no magnetic materials, does not need fluxbusting ever.  MM cartridges, of course, should NEVER be demagnetized, as you may kill the entire beast very quickly.  I have the sameSS-modified Grace, based on a Ruby original.  It is excellent. As long as you don't demag an MM, I don't think you can do harm to an MC by fluxbusting. I use the Cardas test LP once in a while for that purpose.
I use the Cardas Sweep Record every few months and find that it is
worthwhile to do. But my limited understanding is that this is a very
different (and probably more lightweight) process than the demagnetization provided by the Sumiko Fluxbuster and that kind of direct demagnetization, particularly if overdone, can be harmful. 

AJ Van den Hul, for example, strongly recommends against 
demagnetization with stuff like the fluxbuster. 

There are some interesting comments below from JCarr of 
Lyra from a post at Audioasylum.

I was told by Dynavector that their cartridges do not need to be demagnetized. I have a ZYX that I have never demagnetized - sounds fine to me. 
Never is the correct answer. Worse than stupid concept perpetrated by people who have no idea what they are talking about. If you have a reel to reel you can demagnetize your tape heads. If you don't, throw that thing in the garbage. Your going to hurt yourself.
NEVER demagnetize anything which already has a magnet inside it for its normal operation.  Otherwise you will destroy/weaken the magnet.  This includes moving coil, moving magnet cartridges and speakers as well as your credit cards :)
Fluxbuster works fine on HOMCs.
Use it whenever you think it will improve the SQ. No set answer, every system and ears are unique.
Did you get the manual?
Dear @wcheng2 : I still have the same Sumiko you own. I used several years ago and in those old times I thought it makes that the cartridge recovery its " transparency " or something like that.
I used till the fluxbusting damaged one of my cartridges, I can't remember which one, burn-in one of the coil wire and I always followed the Sumiko precise instructions.

In those times I did too with MM taking the cantilever/stylus out.

So it's hard to say if it's safe to do it with LOMC cartridges and if with today designs really makes a recovery " up-date " in the cartridge performance. Maybe I will test it with some of my LOMC cartridges. We will see.

Regards and enjoy the MUSIC NOT DISTORTIONS,
I don’t seriously disagree with those who say never to use a flux buster like the Sumiko. As I mentioned, I only and occasionally use the Cardas test LP for that purpose, and it does seem to rejuvenate MC cartridges. My rationale is that I am fairly sure that playing an LP is not going to damage the magnet in the cartridge. It is probably a very gentle process, if it actually does any good at all. But one cannot say often enough, never demagnetize an MM cartridge. The same probably holds for an MI type, although maybe less dangerous in that case. In fact, I once owned an Aesthetix Janus preamplifier which has a demagnetization circuit that you can switch in. I was so leery of accidentally damaging any of my precious vintage MM cartridges that I disabled that circuit.
Did get the manual but it doesn't mention or recommend time between treatments.  

Thanks for your responses everyone!  I think I'll just try using the fluxbuster every few weeks or so.
Is the primary question not about ''coil core''? Iron core is used
in order to increase the output.'' Coreless'' kinds as the expression
suggest have no ''core''. It is this ''iron core'' which get ''magnetic
saturated'' and may need demagnetisation? 
Nandric and I agree. As to the cardas  test record, I have always felt that the benefits derived from using it are as much due to exercising the cartridge suspension over a wide range of frequencies as they are to any demagnetizing effect.

To the OP: I am surprised that your reading of these responses would lead you to the conclusion that you should use the fluxbuster every few weeks. My reading leads me to conclude that it should not be done frequently and then only for MC cartridges with an iron core coil. I would define “not frequently“ as every six months to a year, at most.