and i'm not sure if I need daily water changes ?
Hi,
There is less oxygen in saltwater then freshwater... so you need water movement,
the HOB is not enough. I keep a 10g for a QT/HT. I use an air line (no stone) attached via rubberband, to the PVC/plastic decoration, to bubble up and move the surface. A 20g would require at least a nano power head, then a regular power head for anything larger then that. Water movement is a must have, the wave is the life of the ocean and your saltwater tank. I'm sure that's why you have had no "luck" with keeping a QT.
I also keep ammonia test strips on hand, they take seconds to test for ammonia ... it doesn't matter what the number is,
any reading at all means do a water change. If I just have a fish in quarantine, and I'm not dosing medication, I add prolifera macroalgae, it not only makes the tank look better, and give the fish a happier hiding place then just a PVC pipe, it helps to keep the water quality pristine.