the type of filtration saltwater uses is VERY different when compared to freshwater systems. a typical saltwater system utilizes a sump, a filter sock (mechanical filtration), a protein skimmer (to removed dissolved proteins), and live rock (biological filtration), with the possible addition of carbon (chemical filtration).
Hang on back filtration, and canister filters, are designed for freshwater, and CLAIM to be able to filter saltwater systems. You are going to need live rock, honestly at this point in the hobby we've all realized LR is not an option... it looks great, and is the best filter you can buy (by far).
You advice, would be to find out the brand of your current 29g tank, and whether or not it is tempered, and then figure out what will work best based on the tank you already have. Many people don't share my opinion, but i guarantee you will feel let down by HOB filters if you decide to go that route.
Also with skimmers, there are so many great skimmers competing in the market that a DIY skimmer is not much cheaper than a very nice manufactured one!
