Apparently the magnetic limescale removers do not work very well, they are only as effective as the distance the electricity produces a magnetic field, which is usually locally.
The limescale in the store tank is probably because the hot water cylinder is backing up the cold feed raising the water temperature. If there is a lot of scale check the hot water pipes for restrictions. It is a problem on direct systems and one of the reasons people use indirect or sealed systems on their heating.
Basically the higher the water temperature the less limescale can be held by the water. So if the water is hot it looks for somewhere to go and usually seems to pick the relatively rough internal surface of pipes.
The magnetic field generated by the electricity aligns the limescale molecules in such a way to stop them from sticking, but once out of range of the magnetic field they are back to what they where. So it does not get rid of limescale it just stops it from sticking.
A base water softener is probably the best as that alters the water, but they are dear and need regular attention. Which if your like me, can be a bit of a nuisance as I prefer to "fit and forget" knowing I will probably forget.
But then technology changes so fast now days it may be worth "Googling" electric limescale devices, but be a bit wary and possibly look for the words inhibitor rather than remover which may indicate that it only helps with limescale it doesn't remove it.
