A couple of thoughts on the canopy/heat. If the tank's in a room with reasonable temperature control (AC in the summer, heat in the winter), and no direct sunlight can hit it, then it's highly unlikely you will require a chiller with T5HO lighting. One typically needs a chiller only if the room temperature gets too high in the summer (over about 76 - 78 deg F), or one is using high intensity metal halide (MH) or MH/T5HO combinations. If you decide to go with LEDs, then yes, you really, really need a PAR meter or access to one (many reef clubs have a "club meter" that they loan out). It's very, very easy to fry corals with the intensity that most LED fixtures can put out, and it's very difficult to judge the intensity of the lighting by eye alone. However, you do not require a PAR meter with T5HO lighting. The nature of fluorescent lighting is that the total PAR that a given lamp puts out is spread over the entire length of the bulb, and it's very, very difficult to get too high of an intensity over the tank as a whole because it's just not possible to fit that many bulbs over a tank. There's a caveat to every "rule", and it might be possible to generate too much intensity with T5HO if one had an extraordinarily shallow tank - 12" or less. There's several reasons that I and others will recommend that you start with a high quality T5HO fixture like you're considering instead of LED lighting. The first is that, as a beginner, the overwhelming complexity of LED lighting can be intimidating. Not only must you figure out how many fixtures you'll require, but there's also the matter of spectrum - most fixtures will let you adjust to a spectrum that won't make corals happy. Then there's the biggest reason - the expense. A coral reef tank is not a cheap endeavor, and there's a quite high initial outlay for not only the tank, live rock and livestock, but also numerous test kits, ATOs, a good skimmer, effective propeller pumps for the tank, a water purification system, etc... Typically, a good T5HO fixture like an ATI is going to set you back about $700 for a 6 foot tank, plus about $160 for bulbs. Lighting a 6 foot tank with EcoTech Radions, AI Hydra 52s, or Kessil AP700s is going to cost a lot more than that. Even cheap chinese LED fixtures aren't all that cheap, and many of them lack sufficient spectrum below about 420 nm. An 8-bulb ATI, and 4 Blue Plus, 2 Purple Plus and a couple of Coral Plus bulbs, and you're set. Simply add a timer to turn the 2 daybreak/twilight bulbs on at 10 a.m., another timer to turn the rest of them on at noon, and then most of them off at 10 p.m., and the final 2 off at 11 p.m. or midnight, and you're all set.
