A canister filter or sump for my 20gal as I’m still using a 45gal HOB filter. it provides good flow to a third of my tank however, so perhaps a wave maker or another circulation pump as well to make up for the lost flow
A probe rack. I started hooking up my apex, dos, and trident yesterday and tried to 3d print a probe rack. It didn't go too well so this evening I'm driving just over 2 hours round trip to buy a magnetic probe rack because I'm too impatient to wait on shipping. Wait... maybe my answer should be patience instead.
Currently needing a t5 light to mount over newly built 30" frag tank, oversized uv scrubber for the 120, and 17 days to tick off the calendar so that fish can come out of the hospital tank and back into the display.
Let’s see for me since my upgrade tank is a massive work in progress (I.e. running water with minimal rock). The most important thing for me is upgraded lighting, looking to get two 250W Metal Halides with either reef brite or t5 supplements