It looks as though you have a couple of power filters and a HOB
canister filter. It also looks like a part of the tank's top rim is missing. I'm not sure I'd trust the tank in that situation.
You'll need a refractometer or hydrometer and at least ammonia, nitrite, nitrate, and pH test kits. For corals, kH
, calcium, phosphate, and magnesium are also a good idea.
If you want corals, you'll need to invest in a good light. Initially, The least expensive viable option (generally speaking) would be a 4 bulb T5 HO
Canisters are also a bit of a pain to maintain a reef with since keeping them clean is paramount to controlling nitrates.