My question is, should I add another 10lb? It seems like it would push the
depth to about 2-3 inches. Also, is it ok to add sand this late into cycle?

i wouldnt DSB's are not as effective in nano's which you have, check out the nano forum on
reefcentral or nano-reefs.com

otherwise adding the sand wont hurt. your not "late into" any cycle. and even if you were
the effects of several small additions wouldnt hurt.

--
Richard Reynolds