When I lived in an area with hard water and had the same issue- I would remove the pieces of equipment and I used vinegar- plain old white distilled vinegar. that did the trick- I hardly had to scrub at all! Of course, please make sure you rinse the equipment REALLY WELL before placing back in the tank.
I have found this to be the safest method to remove that nasty crusty stuff without feeling like me arms were going to fall off from scrubbing!!