im so glad to hear that you already started with RO water and that you plan on getting an rodi unit. this should be your first purchase.
we all know that things can get pretty pricey at first and that it may take time to get better performing equipment.
at the moment, i would suggest purchasing in this order.
1. rodi unit, preferably with a tds meter or get a handheld one
2. refractometer, cant mix saltwater without knowing the proper salinity
3. better test kits. salifert, and hanna seem to be the most accurate
4. 10 ish pounds more live rock or decent dry rock.
5. skimmer. with all the above in place your tank can be sustained with frequent water changes until a skimmer is available.
6. better lighting. with a fish only system the lights are really only for you to see your fish, so what you have will be fine. Once you start getting into coral you will need something better that can provide what they need to thrive.
Most if not all of these items can be found in our classifieds section. If you dont see what you are looking for, post a looking for ad with some sort of price range you are looking at and see who bites. Sometimes we dont consider selling things until we see someone with a need for it. We are all hoarders to some extent. I know i am.
As for the HOB filter, once you move it to your QT, dont ever bring it back to your main tank. Keep everything seperate. Nets, water change buckets, hoses, heaters..... EVERYTHING!!! You've taken the first step and realize that a qt tank is important, dont make it a wasted effort by bringing whatever may have potentially been in your qt by using it on your display.
Thats all i have for now.
