even if you're doing weekly changes, a quick little shot of bionic or even your own stuff probably won't hurt. i've found that even with reef crystals both calcium and alk are pretty low compared to where i want them.
i'd also test after your water change and see what it is.
right now i have xenia,kenya,trumpet,zoo's and shrooms all growing great.
the test kit i have right now doe not test calcium or mag .
do you think the a pet store would test those for me if i bought a sample in?
i would hate to buy to test kits to only find out i am fine and do not need dosing.