First thing to do is get another calcium test kit and double check, they do go off.
One way to increase it is to use a salt mix with raised elements, e.g. Red Sea Coral Pro (black bucket), however that will also affect your alkalinity etc too.
I know you said you don't want to dose but it really is pretty easy even without a dosing pump.
Just get some Red Sea foundation A liquid and follow the dose instructions. You don't need a doser, it really is simple. 1ml increases 100L by 2ppm, so you just multiply that by the size of your tank. Increase it by say 30ppm a day until you reach your target then just dose a small amount by hand each week to keep it stable.
If it's a big tank, then buy the powder version and mix up some stock solutions, works out a lot cheaper.