apply lime scale remover products

In places with "hard" water, home appliances are affected by limescale in pipes and resistors.

For the water heaters it is recommended to use a polyphosphate crystals filter but as dishwashers are using salt I can't see this recommendation.

However for a dishwasher machines having heating problems i can the solution of adding vinegar or lemon juice after 20minutes.

I suppose 20minutes is to ensure that the 1st step of removing previous water has been completed.

Does lime scale remover products work better with low or high temperature?

What product is the stronger?