tank temp

Most people will say to keep a reef around 76-78 degrees. I have a 55 gallon with fish and corals. I have pc lights and acrylic cover so there are no big openings on the top of tank minus the back where the filter and skimmer sit. I have a heater in the back behind some rock I forget how many watts it is but with the tank covered the temp has been able to stay around the 76-78 rang no problem. It really depends on what lighting you have and if you leave the top open or covered..stuff like that.

Usually about 76 is a good temperature to shoot for. You can go up to 80 with little impact to the fish or corals, but higher than that can start to cause issues. Also lower than 72 is also undesirable. If the temp gets to high all you need to do is position some fans to blow on the surface of the water to help increase evaporation. Most of the time that is all that is needed to lower the temp if it gets to hot.

Welcome jameshalt.
I agree with what's been said and will add my 2 cents.
A smaller heater is a good way to prevent a rapid boil. Not that a heater can boil a tank, but the oversize heater heats the water so fast that the hobbyist may not have the time to notice the rising temperature before it puts the tank above 80. Heaters typically stick ON. I use a heater one size below what the manufacturer recommends. In my book a 50-100W heater is just right for a 55 gal.