Recommended calcium supplements?

[Jayfar]

My tap water tested at 31.1 ppm Ca and 9.28 ppm Magnesium. I'm not sure whether that is sufficient or not. I've been alternating, sometimes combining, MSU well water formula (w/o Ca) and K-Lite (which contains 10% Ca). I aim for about 100 ppm Nitrogen at each watering (frequency varies per pot size and medium).

I have been using epsom salts, usually at least monthly, for Mg and Sulphur. What's a good supplement for Ca, if I need it? I see Botanicare Cal-Mag Plus listed on Amazon. Is anyone using this? Is there a cheaper product that will supply just the Calcium in a soluble form that my orchids can use? I see FirstRays has Calcium Nitrate for example, listed for soaking CHC to help remove salt, but I don't know what rate to apply it at as a supplement or whether it's a good form of Ca for root absorption versus Calcium Carbonate.

I've sometimes read of crushed oyster shells or egg shells used for calcium, but on the other hand, I've also read that those don't provide a soluble or useable form of calcium.

Thanks.