There really is no method for someone that doesn't check their levels, the safest would be frequent partial water changes, but that is not likely to keep up with the clams calcium needs. Once dialed in a CA
reactor will lessen the need to test, but as the animals grow their CA
uptake will increase and adjustment will be necessary which means you need more testing
As far as being necessary, no they aren't, in some systems though they are more economical in the long run and again, once dialed in on your tanks needs they are less maintenance.