I have distilled readily available (in my lab, I used a TDS meter on it awhile back and it read 0) and only use that for tank changes/top-offs. The rocks in my tank are fairly old - I've had them for about 3 years now, but the tank itself has only been running (due to a breakage in the last one) for 1.5 months.
I have a skimmer, certainly not THE BEST skimmer (aquac remora pro, with prefilter, mag3), and hope to replace it in the future, but it seems to be doing 'ok' for now.
I'm just concerned about the zoas and sps (only have two sps thankfully). The setosa looks like it's got some of the brown algae growing on it and I know that's a for-sure killer if it doesn't get resolved soon. :\